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**mom****Member**- Registered: 2012-04-25
- Posts: 94

An urn contains 3 yellow marbles and 5 green marbles. One marble is removed, its color noted and not replaced. A second marble is removed and its color noted.

What is the probability that both marbles are yellow

Pr(YY)=3/28

I did 3/8*2/7=3/28

What is the probability that they are both green?

Pr(GG)=5/14

I did 5/8*4/7=5/14

what is the probability that exactly one marble is yellow?

there were two chances of this

I did 3/8*5/7=15/56 and 5/8*3/7=15/56

Do I divide by two for the probability that exactly one marble is yellow?

I am not sure if I have done all of the steps for any of the questions. Can someone look over my work and give me advice?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,400

Hi mom;

The first two are correct.

The third answer I am getting

15 / 28

When stuck for homework type problems. Draw a tree!

Do I divide by two for the probability that exactly one marble is yellow?

You multiply in this case because there are two. The tree will make it clear.

**In mathematics, you don't understand things. You just get used to them.I have the result, but I do not yet know how to get it.All physicists, and a good many quite respectable mathematicians are contemptuous about proof.**

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**mom****Member**- Registered: 2012-04-25
- Posts: 94

I drew the tree. What step did I miss in the third problem?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,400

Hi;

Count up all nodes at the bottom that have exactly one yellow. What do you get?

**In mathematics, you don't understand things. You just get used to them.I have the result, but I do not yet know how to get it.All physicists, and a good many quite respectable mathematicians are contemptuous about proof.**

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**mom****Member**- Registered: 2012-04-25
- Posts: 94

I have 3/7 and 2/7 for the second draw. The first was 3/8

I know that I am doing something wrong

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,400

Hi mom;

Here is the tree the two you need are marked by a rectangle. Please fill in the probabilities.

**In mathematics, you don't understand things. You just get used to them.I have the result, but I do not yet know how to get it.All physicists, and a good many quite respectable mathematicians are contemptuous about proof.**

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**mom****Member**- Registered: 2012-04-25
- Posts: 94

that gives a better image than how they are teaching me. Thank you. I can see it now. They have us do a tree with fractions and I get confused easily.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,400

Did you get the answer you need?

I have the result, but I do not yet know how to get it.

All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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**mom****Member**- Registered: 2012-04-25
- Posts: 94

I did thanks again

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,400

I hope it was 15 / 28.

I have the result, but I do not yet know how to get it.

All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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**mom****Member**- Registered: 2012-04-25
- Posts: 94

sorry was working on a group project. Yes it was 15/28

Thanks again

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,400

Hi;

Your welcome.

I have the result, but I do not yet know how to get it.

All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

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