Im not sure how to approach this...
There are 20 coloured balls in a bag, Two balls are drawn at random and not replaced. The probability of getting two red balls is 3/38. How many of the 20 coloured balls are red?
#huh
crystal solar
last zealotBOT
Im not sure how to approach this...
There are 20 coloured balls in a bag, Two ba...
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crystal solar
you would do something like 3/76 is the probability of getting one red ball right?
crystal solar
Hello, could anyone help me with this?
pallid sequoia
let the number of red balls be x
so lets just say i had a bag of 5 marbles and 3 of them are red whats the odds that i draw 2 red from 2 random draws
fast bolt
you would do something like 3/76 is the probability of getting one red ball righ...
not quite
the second ball has a lower chance of being red than the first, given you just took one of the red balls out
crystal solar
oh true
fast bolt
let the number of red balls be x
so do this
what's the chance that the first one you pull out is red, then
crystal solar
3/38-3/76?
fast bolt
just do it in terms of x
fast bolt
x red balls out of 20 balls
pallid sequoia
okay so lets break down the example for 3 red out of 5 red
pallid sequoia
the number of possibilites for our first draw is 5 possible balls then we have 4 possible balls
then for the cases we want
we first want to pull out any of the 3 red balls then any of the 2 red balls
so we get 3x2 / 5x4
makes sense?
fast bolt
yes
so there are x red balls in 20 total balls
what's the chance that just the first one you pull out is red
fast bolt
yes that's right
crystal solar
ok good
fast bolt
and how many red balls are left
yes
so what's the chance the second one would be red also
fast bolt
and since you are looking for 2 events both to be true, you multiply the probabilities
fast bolt
why multiply
that's just standard probability things
like for example
flip 2 coins, what's the chance they're both tails?
1/2 for the first, 1/2 for the second
crystal solar
oh i see
fast bolt
you want to multiply them to get 1/4, since they're independent and you want them both to be true
crystal solar
got it
fast bolt
so (x/20) x ((x-1)/19)?
anyway, yes
crystal solar
omg this makes so much sense now
I ligit love you i need that i have an exam tomorrow haha
no like thats actually
like
omg
i get it
fast bolt
pallid sequoia
:D nice