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For the first one, I know this is the correct answer, but I don't know how it should be.

I calculated P = 5/11 * 4/10 * 6/9 * 5/8

What am I missing?

First of all 5c2 * 6c2 / 11c4 = 10 * 15 / 330 = 5/11 not 5/22.

You are calculating the probability of just one way of combining 2 whites and 2 reds. If you multiply your solution by the number of ways 2W and 2R can combine (or 4c2) you will get the correct answer. _________________

Best,

AkamaiBrah Former Senior Instructor, Manhattan GMAT and VeritasPrep Vice President, Midtown NYC Investment Bank, Structured Finance IT MFE, Haas School of Business, UC Berkeley, Class of 2005 MBA, Anderson School of Management, UCLA, Class of 1993

For the first one, I know this is the correct answer, but I don't know how it should be.

I calculated P = 5/11 * 4/10 * 6/9 * 5/8

What am I missing?

First of all 5c2 * 6c2 / 11c4 = 10 * 15 / 330 = 5/11 not 5/22.

You are calculating the probability of just one way of combining 2 whites and 2 reds. If you multiply your solution by the number of ways 2W and 2R can combine (or 4c2) you will get the correct answer.

Thank you for your response. The trouble with me is either I get it
completely or not. In this case, I've not got it.

Let us assume that we are taking 4 white balls out of 5 white and 6 red
balls then we say P = 5/11 * 4/10 * 3/9 * 2/8.
Why we need to multiply in with 4C2 if we are choosing more than one
color. Why does the order of picking the balls matter?

For the first one, I know this is the correct answer, but I don't know how it should be.

I calculated P = 5/11 * 4/10 * 6/9 * 5/8

What am I missing?

First of all 5c2 * 6c2 / 11c4 = 10 * 15 / 330 = 5/11 not 5/22.

You are calculating the probability of just one way of combining 2 whites and 2 reds. If you multiply your solution by the number of ways 2W and 2R can combine (or 4c2) you will get the correct answer.

Thank you for your response. The trouble with me is either I get it completely or not. In this case, I've not got it.

Let us assume that we are taking 4 white balls out of 5 white and 6 red balls then we say P = 5/11 * 4/10 * 3/9 * 2/8. Why we need to multiply in with 4C2 if we are choosing more than one color. Why does the order of picking the balls matter?

It doesn't matter. But you are calculating the SPECIFIC probability that the ball will come up in a specific sequence (2R then 2W). Hence, you are missing the other five ways. _________________

Best,

AkamaiBrah Former Senior Instructor, Manhattan GMAT and VeritasPrep Vice President, Midtown NYC Investment Bank, Structured Finance IT MFE, Haas School of Business, UC Berkeley, Class of 2005 MBA, Anderson School of Management, UCLA, Class of 1993

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