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Help on solving a combination problem

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by crackgmat007 » Mon Apr 13, 2009 8:39 pm
Since only Tom or Jerry can be on the committe, I considered Tom & Jerry as 'one' for calucating the combinations. Hence, 6C3 = 20.

Answer seems to be C (30)...am I missing something?
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by kirvar » Mon Apr 13, 2009 9:06 pm
Number of groups with only Tom: 5C2 = 10

Number of groups with only Jerry: 5C2 = 10

Number of groups with neither Jerry nor Tom: 5C3 =10

Total = 30
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by cramya » Mon Apr 13, 2009 9:09 pm
Tom and Jerry are 2 different persons.

One way to do it is to first find the total number of 3 member sub committes possible from 7 people

7C3 = 35

Then find the number of subcomitees in which Tom and Jerry will be there.

2c2( which iequals 1) * 5c1 (once u choose Tom and Jerry u have 5 persons remaining to choose 1 from) = 5


Subtract 2 from 1 which will give u the number of 3 member commitees where Tom and Jerry will not be there

35 - 5

= 30

Regards,
CR
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