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
a = b
a + b = 0
ab = - 1
ab = 1
D.
ab = 1
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