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Re: M15-18 [#permalink]
combinatorics is my weakness but correct my if im wrong, the numerator of the answer should be addition not multiplication that equals 9?

you have 1C3∗1C3∗1C3 / 3C9 = 9/28
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Re: M15-18 [#permalink]
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lydennis8 wrote:
combinatorics is my weakness but correct my if im wrong, the numerator of the answer should be addition not multiplication that equals 9?

you have 1C3∗1C3∗1C3 / 3C9 = 9/28


No, it's multiplication, because of Principle of Multiplication. The result is 27/84, which when reduced gives 9/28.

Principle of Multiplication
If an operation can be performed in ‘m’ ways and when it has been performed in any of these ways, a second operation that can be performed in ‘n’ ways then these two operations can be performed one after the other in ‘m*n’ ways.

Principle of Addition
If an operation can be performed in ‘m’ different ways and another operation in ‘n’ different ways then either of these two operations can be performed in ‘m+n’ ways (provided only one has to be done).

Check below post for more:
Probability Made Easy!

Theory on probability problems

Data Sufficiency Questions on Probability
Problem Solving Questions on Probability

Tough Probability Questions
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Re: M15-18 [#permalink]
I think this is a high-quality question and I agree with explanation. The formula expression is incorrect
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Re: M15-18 [#permalink]
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I have edited the question and the solution by adding more details to enhance its clarity. I hope it is now easier to understand.
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Re M15-18 [#permalink]
I think this is a high-quality question and the explanation isn't clear enough, please elaborate. I understood 3c1, but 3c9 comes out to 84 so shoudnt the ans be 9/84 ( this ans not given in options)? I am nopt able to understand where is 328 coming from
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Re: M15-18 [#permalink]
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Vikramaditya00 wrote:
I think this is a high-quality question and the explanation isn't clear enough, please elaborate. I understood 3c1, but 3c9 comes out to 84 so shoudnt the ans be 9/84 ( this ans not given in options)? I am nopt able to understand where is 328 coming from

­\(P=\frac{C^1_3*C^1_3*C^1_3}{C^3_9}=\)

­\(=\frac{3*3*3}{(\frac{9!}{6!3!})}=\)

­\(=\frac{3*3*3}{7*4*3}=\)

­\(=\frac{9}{28}\)­
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Re: M15-18 [#permalink]
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