Just to clarify:

p = .48 is the probability that an investor has exchange-traded funds in their portfolio.

Thus

p =.52 is the probability that an investor doesnothave exchange-traded funds in their portfolio.

Thus, if you want to find the probabilitythat at most11 peoplehaveexchange funds in their portfolio, you would use:

binomcdf(25, 0.48, 11).

The parameters are (trials, prob of success, max # of successes)

Your answer would have worked if the last parameter meant "at least k successes". But it means -at most- k successes.