Bunuel wrote:
shohm wrote:
Please help understand where my thinking is flawed ?
A 3 member committee needs to be formed from 4 pair of distinct siblings say (b1,s1), (b2, s2), (b3, s3), (b4,s4).
1st member can be any of the 8 persons. Now, for next member selection, discard the pair from which the 1st member was selected. So now we have 3 pairs left to choose from.
2nd member can be any of the 6 persons in the left 3 pairs. Now, for next member selection, discard the pair from which the 1st and 2nd member were selected. So now we have 2 pairs left to choose from.
3rd member can be any of the 4 persons in the remaining 2 pairs.
So total number of ways = 8*6*4 = 192. Where am I counting the extras ?
Check here:
http://gmatclub.com/forum/if-there-are- ... ml#p775925Hope it helps.
Can anyone explain why the below is wrong?
To calculate the numbers of cases that have siblings, we select 2 pairs out of 4 pairs (1 pair included in the committee and only 1 person of the 2nd pair in the committee): 4C2 *2 = 12
Why is this wrong?
If we are calculating the cases with siblings that that means those 3 people belong to 2 pairs, and the 3rd person can either be sister or a brother
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