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#1 2015-04-05 13:45:05

jubadedo
Member
Registered: 2015-04-05
Posts: 19

Probability Questions

Hello guys, sorry to keep pelting you with questions. Again, these questions also keep stumping me.
Jill has a stack of 8 cards consisting of Jack of Spades, Jack of Hearts, Jack of Diamonds, Jack of Clubs, Queen of Spades, Queen of Hearts, Queen of Diamonds, and Queen of Clubs. Jill shuffles the stack then deals out the top 3 cards. What is the probability that two of the cards dealt were Jacks and one was a Queen?

My teacher tells me the answer is 3/7, but I still can't comprehend how he gets to that solution. I keep doing

, but that is not the correct set-up for the problem. I would love it if someone pleased explained how you derive that answer. 

Ellen enters a convenience store. The probability that she buys bread is 60%, the probability that she buys milk is 50%, and the probability that she buys both bread and milk is 30%. What is the probability that she will buy either bread or milk or both? (nearest percent).

I am completely stumped on this one. :*(

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#2 2015-04-05 16:47:47

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

Re: Probability Questions

Hi;

Your teacher is correct, 3 / 7 is the answer and is obtained by using treeing or using the hypergeometric distribution which is designed for this type problem.


In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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#3 2015-04-05 19:46:10

Bob
Administrator
Registered: 2010-06-20
Posts: 10,058

Re: Probability Questions

hi jubadedo

Your answer is for Jack Jack Queen.

But you have two other possibilities: Jack Queen Jack and Queen Jack Jack.

So do this:

(4/8 x 3/7 x 4 x 6) + (4/8 x 4/8 x 3/7) + (4/8 x 4/8 x 3/7) = 1/7 + 1/7 + 1/7

IwCtFsP.gif

You know that the overlapping region has 30% so you can also fill in the (bread no milk) and (milk no bread) regions.  As there must be 100% altogether, you can then fill in the (no bread no milk) region.

Bob


Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob smile

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#4 2016-04-17 02:48:17

thickhead
Member
Registered: 2016-04-16
Posts: 1,086

Re: Probability Questions

Last edited by thickhead (2016-04-17 02:50:54)


{1}Vasudhaiva Kutumakam.{The whole Universe is a family.}
(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha
{Gods rejoice at those places where ladies are respected.}

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