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If 20% of three subsets (i.e., subsets containing exactly three elements) of the set A = {a1, a2, …, an} contain a1, then the value of n is
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15
b
16
c
17
d
18
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Correct option is A
The number of subsets of A containing exactly three elements is nC3 whereas the number of three subsets of A that contain a1 is n−1C2. We are given, n−1C2=20100 nC3⇒ (n−1)(n−2)2=15n(n−1)(n−2)6⇒n=15Similar Questions
is equal to
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