1.

The number of all three element subsets of the set `{a_(1),a_(2),a_(3)......a_(n)}` which contain `a_(3)` , isA. `""^(n)C_(3)`B. `""^(n-1)C_(3)`C. `""^(n-1)C_(2)`D. none of these

Answer» The number of three element subsets contaning `a^(3)` is equal to the number ways of selecting 2 elements out of n-1 elements.
So, the required number of subsets `=""^(n-1)C_(2)`.


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