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05 Aug 2020, 22:10
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VeritasKarishma BrentGMATPrepNow
I was initially inclined to resolve this using the combinatorics approach, but then I tried the below approach. Please let me know if this approach is correct.
Joe can be selected in either of the 3 below slots from a group of N people.
____ ____ ____
Joe ___ ____
___ Joe ____
___ ____ Joe
Probability of selecting Joe from N people is 1/N
Therefore Joe can be selected in 3/N ways.
I was initially inclined to resolve this using the combinatorics approach, but then I tried the below approach. Please let me know if this approach is correct.
Joe can be selected in either of the 3 below slots from a group of N people.
____ ____ ____
Joe ___ ____
___ Joe ____
___ ____ Joe
Probability of selecting Joe from N people is 1/N
Therefore Joe can be selected in 3/N ways.
10 Aug 2020, 03:34
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aritrar4
The question asks for selection only, not arrangements. So there are no slots to arrange Joe in.
You should use (n-1)C2/nC3 = 3/n
(n-1)C2 - Number of ways of selecting Joe and 2 people from leftover (n-1) people.
nC3 - Number of ways of selecting any 3 people from n people.
Say n = 10,
9C2 / 10C3 = (9*8/2) / (10*9*8)/(3*2) = 3/10
23 Aug 2020, 05:41
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gmatkarma20
Why are we first identifying the probability excluding Joe and then using the 1-P formula. Instead cant we just say 3C1 for probability of Joe to be picked. In which case though the probability will be 3/10 and not 3/5. Kindly clarify!
