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gmat pre question

by pradeepkaushal9518 » Fri May 07, 2010 12:11 pm
A certain university will select 1 of 7 candidates eligible to fill a position in the mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in the computer science department. If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?

1.42
2.70
3.140
4.165
5.315
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by clock60 » Fri May 07, 2010 2:19 pm
i got 315

7C1*10C2=315

but it can`t be so simple , what i am missing??
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by shashank.ism » Fri May 07, 2010 10:46 pm
clock60 wrote:i got 315

7C1*10C2=315

but it can`t be so simple , what i am missing??
your answer is correct .
Follow the question , you will find that none of the candidates are eligible for both the posts. That means there are total of 17 candidates out of which 7 are eligible for mathematics department and 10 are for computer science department .

Now for mathematics department we need to choose 1 out of 7 so total number of such ways = 7C1 = 7
and for computer science department we need to choose 2 out of 10 so total number of such ways = 10 C2 = 10x9/2 =45

so total different sets of 3 candidates to fill 3 positions = 45 x 7 = 315

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by pradeepkaushal9518 » Sat May 08, 2010 3:27 am
ya answer is right
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