#help-23
1 messages · Page 303 of 1
I thought your syllabus directly taught you that equation
in that case theres still something easier we can do
originally we have the tangent line (y - h(k)) = h'(k) (x - k)
but i feel like the equation ur giving me is gonna be easier to use
now if you move the - h(k) to the other side, you get the y = h'(k) (x - k) + h(k) equation
this is a common way to write the tangent line equation
omg cool
not necessarily
oh wait wha
youre forgetting that its not in y = mx + b form
its got an (x - k) there
we'll need to address that
ohh ye
also, usually the tangent line equation is shown online as $y=f'(a)(x-a)+f(a)$ for a tangent line at $(a, f(a))$
mtt
commonly the function is f, and the point's x-coordinate is either a or c
if youre memorizing the equation, the convention is this one
oh oka
we're using the equation for our purposes, so our function is h and our coordinates are (k, h(k))
okaoka
now with y = h'(k) (x - k) + h(k),
you can expand (use distributive property on that h'(k) (x - k)
so h'(k) x - h'(k)k +h(k)
yep
okaa
now the slope is h'(k)
and the y-intercept is h(k) - k h'(k) as shown by what you typed
okaa
now you can put in -k in and see what happens
okaa
y = h'(k) x - h'(k)k +h(k)
y= m x + c
h(k) is even so h'(k) is odd and h'(-k) = -h'(k)
h(k) is even so h(-k) = h(k)
y= h'(-k) x - h'(-k) (-k) +h(-k)
y= - h'(k) x - h'(k) (-k) + h(k)
=- h'(k) x + h'(k) (k) + h(k)
so y = -mx + c
is that right
unfortunately it isnt
first youre beginning with y = mx + c instead of y = mx - c
around the - h'(-k) (-k) part, the next line says - h'(k) (-k)
oh shoot didn't carry the negative in
y= h'(-k) x - h'(-k) (-k) +h(-k)
y= - h'(k) x + h'(k) (-k) + h(k)
neg neg
right
yes
so y = h'(k) x - h'(k)k +h(k)
y= m x + c
h(k) is even so h'(k) is odd and h'(-k) = -h'(k)
h(k) is even so h(-k) = h(k)
y= h'(-k) x - h'(-k) (-k) +h(-k)
y= - h'(k) x + h'(k) (-k) + h(k)
=- h'(k) x - h'(k) (k) + h(k)
so y = -mx + c
yep
np
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A test consists of 100 questions. A student gets 4, -1, or 0 marks, if he answers a question correctly, wrongly, or leave it blank, respectively. How many different total marks of the test are there?
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can someone help me with vector
If AB = u, and AF = v. Determine vector of DF
here's my guest
DC = FA = -AF = -v
CO = BA = -AB = -u
DF = DC + 2CO = (-v) + 2(-u)
is that correct?
i need someone actually know the answer, and i have some question
This is a regular hexagon?
yes
seems right
im no mod but i dont think ur suppose to ping for helpers until 15mins later...
rite? but i see another answer with DO and OF then include DE and so on
i didnt know that, sorry
i think DF= -v -2u, which u have gotten
it makes sense
it should eventually end up with -v -2u as the final result
u should end up with -2u-v whichever way u do
theres many ways u could go about for it
the way u did it is just i would say the fastest way?
mhmm
like DO or DE
bc anyway u go, u will eventually reach -v -2u
u can but itll be quite longer
ur way is faster and more convenient
so it will be a triangle?
sorry?
if u do that, u would be finding DE
it would be from E to F*
so yeah, why is it reach to C?
D to O to E to F will give DF
huh?
D to C is like why is it line up to C and not to
D to F instead and count it normally ( but still i dont get it with hexagon thing)
in order to get from D to F, u can go from D to C to O to F, and it will give DF
sorry i dont get what ur trying to ask
bad thing discord mobile cant draw
r u trying to ask why we do this?
yeah, wait i'll check on my computer 1 minute
here
this is what am i trying to ask, why we dont do this
if u do that, how are u able to find the vector for it?
itll be too hard with what we are given with right?
vectors is like if u wanna get from a certain point to anohter point, u can use vectors where u follow the given paths until u reach ur point
i mean, firstly when i try to find the vector was like that
for the green parts, notice how CO is the same as AB but in the opposite direction, since we know AB = u, then CO is -u, and it happens twice, so thats why we minus u twice
i was like nuh uh, this is got me confusing
is there any other way?
try reading this and see if it makes sense
how so?
if u want to try doing it with the red way, i dont think it’s possible as we cant find what red vector is since there is no vector and values we can work with from the question
ig qns like these, to solve it u would want to try find a path to get from where u want to go, by following other vectors and adding them up!
i see, so we just follow the instruction of the question? and try find a path
mhmmm!
like find a similiar AF and AB and determine the vector ( consider the direction )
okok i got this, thank you boss
appreciate it
yes, do note, these "similar" vectors only work or like AF is only thr same as CB is bc theyre parallel, and have the same direction or opposite direction
so like AF and AO arent the same vector bc it goes into 2 diff directions that arent opposite directions and arent parallel at all
mhmm yea it makes sense, its like a puzzle then
altho u can see that AF and CD are parallel and only thing different about the direction is its going opposite sides
so thats why i deicded to make a path thru D to C to O to F, so i also dont need to deal with vectors going in the direction of AO
yess
no worries 🔥
yuhhh
does it make sense now?
yessir
hurray
do you mind, if i add you to ask more question?
suree
appreciate it, man i wanna learn something
yes pls, and how do i close this help section?
oki, accept my friend request, ive already sent it to u
uh okay?
.close
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is it "valid" to show lim x->inf of sin(x)/exp(x) = 0 by claiming sin(x) will always be in range -1 to 1 for all real input and then that e^-x goes to 0 and since any real "a" * 0 is 0 it's all 0? or some similar reasoning
or would real proof use the Taylor series or something like that
i mean it depends on what u mean by "valid", like yeah, that is the intuition for why it tends to 0
so like if ur doing i.e. a physics/engineering course, that would probs be sufficient
however if ur doing something like analysis that's basically it, but i would write it out properly
like this ^
but it's not rigorous right
got it
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Can we do this together: THere are 4 races in total which have a winner and 10 participants. What are the possible total results if we only look at races won
basically after each race the winners we pick reset
and the order does not matter i guess
WE got 10 participants so: A B C D E F G H I J
Basically asking how many possibilities we can build out of those. Like ACDJ for example
this formula?
$$\binom{10+4-1}{4}$$
Jaeger
like you use this one one group might have 0 objects
this one is valid when groups might have 0 objects in them
for this ques that is not possible as
"each race has a winner"
so you just subtract the number of "fixed" objects from the top
in this case 10 + 4 - 1 - 4
wdym resets?
no i dont think that is the case
more like 10 ppl divided into 4 groups with no repetition
then one winner out of each group
is this exactly the question statement?
yeah it was the question. 10 participants and we do 4 races. Only wins matter. What are the possible chances of the winners
Can be anything like AAAA AABC etc
i mean it is kinda vague
like how are the races conducted?
and what does "only wins matter" mean
@half briar Has your question been resolved?
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Someone help me with derivatives please. Ive been stuck looking at my page for hours because I cannot seem to understsnd
send the sum
Both E and F
For E I understand that it equals to sin (x+y)
But why isnt the derivative cos(x+y) • y'
using chain rule
no it will be cos(x+y)
But I thought you had to use chain rule and multiply the inside afterwards
The answer is -1 btw
Yes
lemme get a paper hodl
I got that
ok how pls
Could you help me with F) as well
I can show you my work but my answer is slightly different for some reason
cos x-2sinx2x-2y /2x
what
answer
mine is correct
why would this not work
no i did not
its 2 dy/dx
He has the right answer idk how
Can you show your work maybe
mine is correct 😭
well its somehow correct
Yeah can you show how you got it
Thats wrong tho
u j have to write sin first then thr cos term
is x times dy/dx not just 1?
because derivative of x = 1?
why wouldnt 2xy = 2 (dy/dx)
it is 1
correct
buddy cmon i solved it i dont get what ur cribbin on
Yeah but my answer key says theres a -2y and x somewhere
You got it wrong bru
Ive said this like 100 times
IDIDNOT
Yes you did man the answer key dont lie
cuz yall did not use rhe term
Oh wait
Product rule
I see it
I got it thanks
In the answer there is no negative
Is there another negative sign im missing for I)?
i
also how is the apart of the derivative of sin^4(2-x)^-1 just cos (2-x)^-1
why wouldnt it be like cos^4 or smt
Its like (2-x)^-1
so it would be 3sin^4(2-x)^-1
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N1 and N2 are norms
how do i prove that Cn exists?
Cn>0
<@&286206848099549185>
I'm thinking about this, but you might want to try in #real-complex-analysis
are you doing it now?
Yes, though I might need some time
ok im gonna wait for you thanks
What's your book's notation for $\R_n[X]$ mean
riemann
polynomial with real coeff and degree at most n
yea that's important to tell
ok
@graceful widget Has your question been resolved?
(I was unable to figure it so far and I have to go, see my previous advice)
ok thank you 
@plucky elk hello just in case
no
if you're not doing anything, i suggest doing it for small n like 1 and 2 to see how both sides evaluate to try to find a pattern
you mean we do it together
but i dont know how to do it
.
do you know what p looks like for n=1 ?
no
what's a polynomial with degree at most 1
yes aX+b
plug that into both sides
ok i will do it but just a question, is Cn changing depending on n?
C_n is notation for a constant that depends on n
ok
on the left side it's a²/3 + ab/2 + b² and the right side it's a²/4 + ab + b²
no i was wrong in my first answer
a²/3 + ab/2 + b² and the right side it's a²/4 + ab + b²
i see that it is smaller
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How do I know which interval makes it true
u know multiplying two positive numbers or two negative numbers is > 0. if one is positive and the other is negative then it is < 0
So you plug in the solutions into the problem above?
If a number is less than zero then it is ||negative||
no
ok easier example, (5)/(-3) is < 0 and (-5)/(3) < 0
but (5)/(3) > 0 and (-5)/(-3) > 0
ok
so u need [x+2 <=0 and 4x > 0 ] or [x+2 >= 0 and 4x < 0]. do you see why?
Because if it’s zero in the denominator then it’s undefined
ok that is also true
but i meant that n/d <= 0 if [n<=0 and d>0] or [n>=0 and d<0]
it means that one number is positive (+) and the other is negative (-), so the multiplication is negative (+- -> -) idk if i explain myself correctly
yes
so basically u need (top >= 0 and at the same time bottom < 0) or ( top <= 0 and at the same time bottom > 0)
Does that always apply
i think ur not getting how im trying to explain it
+/- is negative and -/+ is negative
+/+ is positive and -/- is positive
I know
okay how would you solve it
Look at the 2 intervals that result in a positive fraction
and use those number
[-2,0)
oh i didnt see the whole image
u didnt even need what i yapped, and btw i think u meant negative cuz u want the fraction <= 0
but yes, that happens in [-2,0) because the image says -1/4 <= 0
so u already know the answer
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How do I find the mean?
Yup. 👍
int[0,10] (x*f(x)) dx
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A ball of mass $m$ dropped from a distance $d$ above a plate attached to a spring with spring constant $k$ compresses the spring a distance $x$.
Jash
Derive an expression for x, the distance the spring compresses as a result of the interaction with the ball.
energy conservation
Jash
make a scheme of the situation maybe you will see it better, I don't really understand here
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Trying to study for my test that's coming up, and on the review this problem came up which is very confusing. It's part of the autonomous equations, but the book and lecture don't really cover too much of it, or what "absent harvesting" means, or what a condition would mean towards the problem.
So what I do know: The logistic equation I have been taught goes by:
dx/dt = kx(M-x)+-h
where k is a constant based on the yearly renewal of the population, M is the carrying capacity, x is the population.
I know generally, expanding out the equation and setting up the quadratic equation is helpful, as I'd want the radical to end up being 0. Now, a few issues. It says absent harvesting, but then it says the lake is opening to fishing. So I'm assuming the equation is now what it is, but +-h, where I am solving for h?
As for y(0), I think that means that when t=0, y=1280? I'm honestly not sure with this one, because the lecture or homework didn't really go over conditional statements.
If anyone knows a good way to explain this problem to me, that'd be greatly appreciated.
I mean you seem to have a decent idea of what to do here, there's just one little thing
Now, a few issues. It says absent harvesting, but then it says the lake is opening to fishing. So I'm assuming the equation is now what it is, but +-h, where I am solving for h?
Yes, but it's not +-h, it's just -h. h is a harvest rate, it's a rate of fish you're removing out of the lake
I see, it's specified it's 100% going to be harvesting, so it's -h in this scenario
then the goal is to see how high you can push h so that the equation still has an equilibrium
i.e. what's the highest value of h for which kx(M-x)-h = 0 has a solution ?
or to use the notations in the question replace kx(M-x)-h by 0.06y(1-y/3600) - h
Okay, I see. I went ahead and set everything up
Lemme send a screenshot
Now is that my answer, or do I have to do something with this answer
This is as far as I usually get with this problem
there's a ton of small errors here and there but you fall on your feet in the end at least
also +57 not -57
Where are the errors
Ah I see that now
Any other ones other than the small one at the end?
Ahh I left the +- sign in as a habit
So what I did on the third step of the run is I changed all the signs
which is why h comes out at a positive number
most of these signs don't matter in the end tbf
Yeah would probably have been helpful for me not to continue writing the +- like that lol and yeah it doesn't matter too much, I just did it to keep the lead term positive
Made it look better
But anyways, now what should be done?
Okay that's the missing link
I do not know what the initial condition means in relation to the question
I can only assume it just means the initial population at the start of harvest is 1280
yes
the idea is
here's your function for some h < 57, you get two equilibrium points (approx 800 and 3000 here)
problem is
if the initial population is less than 800, what happens to the population ?
h = 38.7?
But if the initial population is less than 800, then the population would be on an incline
incline ?
you're sure about that ?
this graph is dy/dt as a function of y
so if y is less than 800, dy/dt is negative
I'm not sure
well I just told you no
okay so questions
What's h=38.7 in this scenario
Oh wait
That's probably the answer
Okay
also it's not the answer
Ah yeah I see now
I did my calculation wrong
When it is less than 800, it is on a decline
this is what I've been drawing here, not the actual evolution of the population
Oh
the f(y) plot at least
Okay let me try again
but you should be able to infer the phase line from that
Is 800 half-stable
unstable
Ahh yes
i see it now
Originally I did not connect the phase line because I'm used to it being a vertical line
But if I start at 0, it is negative, or decreases when it's less than 800, and increases when it is greater than 800
which is unstable
Is that correct?
yes
so the problem is that if you start your population at < 800, the population will go straight down to -infinity
i.e. you don't reach an equilibrium
Yes
So maybe instead
This looks like it's in the form of a typical population equation
Would this ones equilibriums be 0 and 3800? Or do I calculate them in the quadratic equation
for h = 0, yes that's the equilibriums
Ahh yes you're right
but you still want to do something w/ the quadratic equation
So I need to use the quadratic for the new equilibriums
yes
And is this for h=57?
what is ?
Sorry
In the quadratic equation, am I assuming the harvest rate is what I found?
So the radical would be 0?
radical = 0 just tells you whether there are equilibriums or not
we want something more precise than that though
I'll increase h a little bit on my graph and you'll see
ok h=53.4
you still have 2 equilibriums, approx 1400 and 2400
what happens if you start at 1280 now ?
yeah and we don't want the population to decline when we start at 1280
If the population is 1280 at y(0)
Would I find h by setting the equation = 0 when = 1280?
And then run my quadratic using that harvesting number for that population to find my equilibriums?
I see the point now though
I want it to be in equilibrium with 1280
you want 1280 to be between the two equilibriums yea
the quadratic formula gives you the two equilibriums
or at least you want it to be bigger than the smaller equilibrium
Okay
otherwise you end up with a "goes to -infinity" situation
the phase line doesn't change very much really, it's just the equlibrium points that move
I'm just confused on the quadratic formula part
h=57 would obviously set the radical to 0 and obviously give me 228/0.12 +- 0
Which is reflected in the graph as the vertex
1900
but that means if I'm at 1280, it's another -infinity issue
yeah
so you don't want h=57
you'll want something smaller
you want h such that you end up in the 3rd situation
Oh
If 228/0.12 is 1900, then the radical needs to be equal to (1900-1280)^2?
so that 228-sqrt()/0.12 is 1280, and then I can find 228+ using that same number?
228-sqrt()/0.12 is 1280
ok yeah
I'm sure that's a method, is that the best method to deal with this though?
Felt a little weird to me
this is prolly the most natural way
"I want 1280 to be between the two equilibria, so I solve for the two equilibria and find the biggest h for which 1280 is between the two"
it's not like there's a completely wild step going on here
Okay
Ah wait I did my logic incorrect
If 1280/0.12 is 1900, then I simply need the minus term to be 620 but I have to account for the 0.12 on the bottom
So the radical needs to be like 74.4
,calc 0.12*(1900-1280)
Result:
74.4
yea
So with that, I set up my equation 51984-912h = 74.4^2. Solve for h, and I got that my value of h is 50.930, or 51 fish of harvesting?
yeah
Okay
Yesss
Thank you thank you thank you
That was a tricky one but I feel like you helped me understand it
I hope you have an amazing rest of your day and I appreciate all the help you gave me
🫡
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Just need someone to verify if I’ve done these correct
@full quarry Has your question been resolved?
<@&286206848099549185>
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let $f : \mathbb{V} \to \mathbb{V}$ such that $M_{B}(f) = \begin{pmatrix} 1 & 4 & -5 \ 2 & 1 & 0 \ 0 & 3 & 1 \end{pmatrix}$ and let $B = {v_1, v_2, v_3}$ and $B' = {-v_1 + v_2 - v_3, v_1 + 2v_3, v_2 }$ bases of $\mathbb{V}$. Find $M_{B'B}(f), M_{BB'}(f)$ and $M_{B'}(f)$
938c2cc0dcc05f2b68c4287040cfcf71
@spiral saddle Has your question been resolved?
<@&286206848099549185>
@spiral saddle Has your question been resolved?
<@&286206848099549185>
<@&286206848099549185>
<@&286206848099549185>
@spiral saddle Has your question been resolved?
<@&286206848099549185>
what
help
let $f : \mathbb{V} \to \mathbb{V}$ such that $M_{B}(f) = \begin{pmatrix} 1 & 4 & -5 \ 2 & 1 & 0 \ 0 & 3 & 1 \end{pmatrix}$ and let $B = {v_1, v_2, v_3}$ and $B' = {-v_1 + v_2 - v_3, v_1 + 2v_3, v_2 }$ bases of $\mathbb{V}$. Find $M_{B'B}(f), M_{BB'}(f)$ and $M_{B'}(f)$
938c2cc0dcc05f2b68c4287040cfcf71
idk sry
is oki
how are the M's defined?
\textbf{Property (base changes in the matrix of a linear transformation):}
Let ( B_V ) and ( B'_V ) be bases of a vector space ( \mathbb{V} ) and ( B_W ) and ( B'_W ) be bases of a vector space ( \mathbb{W} ). If ( f : \mathbb{V} \to \mathbb{W} ) is a linear transformation, then:
[
M_{B'W B'V}(f) = C{B'W B_W} \cdot M{B_W B_V}(f) \cdot C{B_V B'_V}.
]
938c2cc0dcc05f2b68c4287040cfcf71
like this i think
this doesnt tell me how M is defined
well ik the concept but the order of subscripts isnt universal so i'd like it clarified
ah this suggests subscripts go right to left
like we need to derive the change of basis matrix formula for each M i think¡
just write it down and compute it later
its good write the solution symbolically before computing anything
to write down the formula for M B'B I need to know what C is doe
but that is my issue, finding the formulas for the matrix representations
yes but you can just write down an equation using C
938c2cc0dcc05f2b68c4287040cfcf71
like maybe like this but im not sure tbh
whats E
like standard basis
oh right im sorry
,, M_{B'W B'V}(f) = C{B'W B_W} \cdot M{B_W B_V}(f) \cdot C{B_V B'_V}.
938c2cc0dcc05f2b68c4287040cfcf71
domain and codomain are V
,, M_{B_VB'V}(f) = C{B_V B_V} \cdot M_{B_V B_V} (f) \cdot C_{B_V B'_V}
oh my, I messed up wait a moment
938c2cc0dcc05f2b68c4287040cfcf71
general tip for math, always try to understand the form of a rule instead of the exact letters
i think the best way to understand change of basis is the right to left order of subscripts
back to the general rule
what do you mean right to left subscripts}
change of basis tells us there are two ways to compute f(x)
the first way is direct via $[f(x)]_{B'W}=M{B'_WB'V}(f)[x]{B'_V}$
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
agree?
oh my
have you seen this property?
do you know what [x]_B means
coordinate of x with respect to basis B?
yes
is this the first way ?
this property is a generalized version of standard matrix for linear maps R^n->R^m
right to left subscripts?
ill get to that later
okok
standard matrix for linear map f:R^n->R^m satisfy f(x)=Ax yes?
but now for f:V->W the matrix product no longer makes sense
mmm
we compensate by using coordinates
how
hence this
you can see it still roughly follows the form of f(x)=Mx
well back here its "image=matrix*input"
here its "coords of image=matrix*coords of input"
matrix change of basis input basis of domain B' with domain W and output basis B' with codomain V of linear transformation f multiplied by coordinates of x with respect to basis B'
something like that?
is a mouthful
my phrasing is more succinct, having all those variables kinda clutters the meaning
sure but why B'_V
like output basis of the matrix representation must match
in order to be multiplied
x is in V so it only makes sense to use a basis of V for coordinates
tbh i can restate the rule without the primes, no difference
yes
the primes only exist to properly state change of basis
$[f(x)]{B_W}=M{B_WB_V}(f)[x]_{B_V}$
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
ok is this clear now?
what now?
if its still not fully clear i would go back to these two messages
I hate it the subscripts V and W make everything like 10 times more confusing
.
.
but you can do that later
ok we're back to this
this tells us there are two ways to compute f(x)
the first way is direct via $[f(x)]_{B'W}=M{B'_WB'V}(f)[x]{B'_V}$
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
the second way is indirect via [[f(x)]{B'W}=C{B'WB_W}M{B_WB_V}(f)C{B_VB'V}[x]{B'_V}]
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
i rewrote the RHS using the change of basis rule
.
LHS aswell
i didnt
??
ohh you modified the RHS by multiplying with
okay that's way better
[x]_{B'v}
okay now what?
now this is where the understanding of the rule comes from
we apply the effect of each matrix to [x] going right to left
and the subscripts guide us
the first product is $C_{B_VB'V}[x]{B'V}=[x]{B_V}$
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
right to left
the second product is $M_{B_WB_V}(f)[x]{B_V}=[f(x)]{B_W}$
okay
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
the last product is $C_{B'WB_W}[f(x)]{B_W}=[f(x)]_{B'_W}$
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
this verifies the indirect way of computing f(x)
remember, the understanding of change of basis is the right to left effect of matrices guided by subscripts
use this whenever writing down the appropriate change of basis for a problem
actually i think its even better if i show this in a diagram
@spiral saddle
im going in a bit so ill leave you this
what you specifically do for problems is pick the matrix product so that the basis subscripts line up correctly
ok
I will come back tomorrow to finish this, thank u fir the definitions
like I feel so tired I was falling sleep
for example $M_{B'B}(f) = C_{B'B} M_{BB}(f) C_{BB}$
𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤
and try to understand how i applied my tip to write this
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Confused on what to do next
,rotate
@split fulcrum Has your question been resolved?
use ref sheet for normal distribution, in their 30s is essentially between 30-40
notice how its also between z score of -1 and 1
also hi again lol
and in 40s would be ppl between age of 40-50 which if u keep drawing the curve itll be z score of 1 to 3
😭 this normal distribution shit killing my confidence
try attempting the qn knowing these facts, maybe itll make it a lot clearer
ur doing hsc too?
yeh
ohhh nice
bro i actually hate this so much bruh i tried doing some financial maths questions from the previous hsc papers too and i cant do shit 😭 💀 its joever
chill chill dont stress
do you have a routine/working out process for finance questions?
they tend to fall similar to each other in some way or the other, being AP or GP mostly
dont ask me about FV and PV stuff, i just guessed those questions when i did adv last year
(bad student)
no not really except i try to use the recurrence relation stuff but i think i have a hard time understanding whats going on in the question
but im confused between 30 to 40 isnt that like 10 standard deviations cuz the question says a std of 5 yrs
yes
remember the rules
between -1 and 1 is 68%
-2 and 2 is 95%
and so on
35 is mean, if thats what u are confused
use this fact to ur advantage!
z score tells u how many standard deviation a particular 'event' is from the mean
pick up ext ur never gonna see financial again lol /kidding
percentage?
like 36 years old
but the people aged between 30-40s isnt that 10 standard deviations but the normal distribution curve only goes to like 3 standard deviations
nah i think u mistaken it for the years between it
one standard deviation = 5 year difference
so ig 10 year difference is 2 standard deviations away from each other (technically)
thats 2 standard deviations from in total
but they are respectively 1 standard deviation from the mean
1 z-score = 1 standard deviation
z-score could be thought of as the 'unit' for how many standard deviations
ohhhhh ok
yuhhh
so um how do we use this to help us?
since we know now that ppl in their 30s makes up 68% of the ppl in the league
u can use that fact to find the exact amount of ppl in the 30s now right?
we know the total is 10000 ppl
and 68% of that is ppl in their 30s
so what do u think u can do to find the exact amount of ppl in their 30s?
so 10,000 * 68%
yussss
not quite
so from the mean its 3 std
specifically which 2 stdanrd deviations
think about it geometrically
draw out the normal distribution curve if need be
think about which part of the graph is inclued in the 40-50
range
uh
ill suggest finishing that curve
i dont understand
remember one standard deviation is 5 years
is it 50 years after the 40?
notice this graph here (its on ref sheet) the 0 essentially means that at thay point it is the mean, the 1 from 0, means its one standard deviation to the right, ig u can think of the negative as in the other direction, its one stdanrd deviation to the left, the 2 means 2 standard deviations to the right of the mean and so on yeah?
yus
the 2nd standard deviation should be 45, not 50
as each stadnard deviation is 5 years right?
so if it is 40 years at the 1st stdanrd deviation, u need to add 5 to get the the 2nd stadnard deviation right?
and another 5 to the 3rd
yes
so far so good?
yeah
so first of all we know that terms 6800 ppl in their 30s
we want to find how many ppl r on their 40s
with the info we have rn we are able to calculate the percentages of ppl in their 40%
take a look at the curve and tell me between which deviations are ppl aged in their 40s r between
wiht this, what is the % of ppl in their 40s
15.85%
yessss
now with that
u can use it to find the ppl in their 40s yeah
which isssss
u tell me
1585 people
yuhhh
now back to the qn
we want to find the difference in amount of ppl right
so what do u do now?
subtract 6800-1585 = 5215
@junior smelt hello 
eating dinner
ye it is
lmao at 11pm
shhhh
what do u notice about it
is this just the portion of people who are 50 or over technically
(i got this part of the qn wrong before its okay)

tbh i thought it was that too
but
it is
but isnt
what 😭
percentage of people aged 40 or over who are also 50 or over
im not a fan of thr wording
what does this mean
do they want me to find like
the number of people in between
or something
nope
its like
out ouf the people whos aged 40+, how many of them are 50+
(dont be like me who just thought i just needed to find how many ppl are over 50+) and divided it by 10000
well the % of it
but thats just the amount of people who are 50+ cuz technically theyre 40+ 😭
the question is basically asking, find the % of ppl aged 50+ but u divided by by the % of ppl aged 40+
as much i would like to say yes it isnt
ie % of ppl aged 50+ OUT OF % of ppl aged 40+
does this kinda make sense
which part doesnt
so it wants to know like
ill try to explain
out of the people who are 40+ it wants to know how many of those 40+ people are also over 50+
this
isnt the smae as this
ya i realize now
yeyeye
bro they put this qn in my trials but changed the numbers
and part b
i got a 0
bc i just thought isnt it just the amount of ppl over 50
out of the total amount of ppl in the league
so sad
anyways
lmfaoo
try giving it a go
so people aged 40 or over have z>1
correct
r u sure>
how did u get 34%
is it 16%
yeah
remember its only 68% if its between -1 and 1 right
so if u half it
only half of it is 34% ie from 0 to 1 or -1 to 0 is 34%
notice how from 0-1 it is indeed 34%, but that saying its not z>1 right?
yeah
yess
another way is that
0 is the middle point
everything to thr right of it is 50%
everyone to the left of it is 50% too
overall making up 100%
so if yk from 0 to 1 is 34%
z>1 is the rest of it
u can just do 50-34
to get z>1
yayy
this way also works
js longer
time is precious in the hsc!
anyways
we now know that 16% of the total makes up z>1 aka ppl aged 40+
what would u do next?
correct
yes
u got one part done
so now we need to find how many ppl are >50 right?
yeah
ur nearly there!
yeah?
and there are 1600 people who are over 40
lock in
bro go do extension 2 😭
lock in bro
does that mean i can take the inbetween of people over 40 and people who are 40
lock in pls
could u explain it more?
okay wait let me draw a diagram
im gonna need some context 
i think i can see what u might be trying to do but thers a shorte way
read this again