PS (Counting Methods) : PS Archive
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PS (Counting Methods)

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13 Dec 2008, 10:04
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A student has to answer 7 out of 10 questions in an examination. If at least 3 of the first 5 questions have to be answered, how many ways can the questions be answered?

A) 20
B) 30
C) 110
D) 40
E) 10
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Joined: 07 Nov 2007
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Location: New York
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13 Dec 2008, 10:17
netcaesar wrote:
A student has to answer 7 out of 10 questions in an examination. If at least 3 of the first 5 questions have to be answered, how many ways can the questions be answered?

A) 20
B) 30
C) 110
D) 40
E) 10

5C3*5C4 + 5C4*5C3+5C5*5C2
= 10*5 + 5*10 + 1*10 =110

C
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13 Dec 2008, 11:12
scthakur wrote:
x2suresh, I think you meant C.

You are right.. thanks. I modified the original post.
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Re: PS (Counting Methods)   [#permalink] 13 Dec 2008, 11:12
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