#need help with stats

83 messages · Page 1 of 1 (latest)

desert charm
ancient dawnBOT
desert charm
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dont understand how to solve part c

stuck olive
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There are two distinct ways to do this, choose 2 girls and 1 boy, and choose 2 boys and 1 girl. Because these are completely separate, you won't double count, so you can just add them

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@desert charm

desert charm
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o

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so..

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wdym by double counting

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oh

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i know

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yes

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you add them

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together and devide by 2

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interesting

stuck olive
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No division

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What I mean by double counting is if you consider the same situation two different ways.

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But this doesn't occur with this approach

desert charm
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i understand

stuck olive
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(if it did you would isolate the number of double counted situations, and subtract them out)

desert charm
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if there was 4 delegates instead of 3 for example, and 1 had to be boy and one had to be girl, would you still have to go through every combination and add them to eachother?

stuck olive
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That would be one way to do it.

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If you had like, 1000 students, 667 male, 333 female, 100 delegates, and required at least one boy and one girl, it would likely be more simple to count all combinations of delegates and then exclude the ones that do not match

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1000C100 - 667C100 - 333C100

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You could also use this approach for this problem

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But I judged it easier to calculate just one more piece of information, considering you calculated the other half in part b

desert charm
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thats amazing

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thanks

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15C3 - 10C3 - 5C3 gives same answer

stuck olive
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Indeed it should 🙂

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A good way to check your work

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If your doubts are cleared up don't forget to mark the thread as .solved

desert charm
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one more for you

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i learnt probablity = n(E)/n(S)

stuck olive
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Exactly

desert charm
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but i dont know what numbers are in each

stuck olive
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So how many ways can you choose 2 of the 10 bottles?

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That's n(S)

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Your probability space

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Then you just need to find n(E) your event space for each of the parts

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Which will be similar to the previous problem

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As a hint, for part c, rather than doing each possibility individually, you can use the compliment of part b

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(because if the two bottles are not the same color, then they must be different colors)

desert charm
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ohh

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i did 5C2/10C2

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for a

stuck olive
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Looks good to me!

desert charm
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i got 14/45 for b

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oh

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31?

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i get it

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31/45

stuck olive
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The compliment of an event space E is the space of events where E doesn't occur.

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Yeah if 14/45 is right for b, then 31/45 would be right for c.

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I haven't checked the math explicitly, I'm just using a phone.

desert charm
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if you were not to use compliment

stuck olive
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But your understanding of compliment is correct

desert charm
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how would you do it

stuck olive
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You could enumerate all of the possibilities, so one green and one blue, one green and one yellow, and one blue and one yellow, then calculate each: (5C1 * 3C1 + ...)

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You do wind up with 31 in that case

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15 + 10 + 6

desert charm
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yep got that

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im doing more quesitons ill come back if i need help

desert charm
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for a

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the answer is 1/10

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how is the event space 1?

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i got the sample space

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@stuck olive

stuck olive
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There is a sample space of 5C2 = 10. And there's an event space of 3C2 = 3

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Should be 3/10

desert charm
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for a?

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why is it 3C2

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oo

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i got it

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2C2/5C2

stuck olive
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For c, d, and e the sample space is slightly different because now order matters for the selection, as we can distinguish chair and vice chair

desert charm
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oh thats true

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never thought that

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@stuck olive got all the other questions correct

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thanks a lot for helping me understand it

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.close