If (1 + x)15 = a0 + a1x + ... + a15x15, then is equal to
110
115
120
135
C.
120
If the coefficients of rth and (r + 1)th terms in the expansion of (3 + 7x)29 are equal, then r is equal to
14
15
18
21
Suppose X follows a binomial distribution with parameters n and p, where 0 < p < 1. If is independent of n for every r, then p is equal to