A study by the Center for Financial Services Innovation showed that only 64% of U.S. income earners

Question:

A study by the Center for Financial Services Innovation showed that only 64% of U.S. income earners aged 15 and older had bank accounts (A. Carrns, "Banks Court a New Client," TheWall Street Journal, March 16, 2007, p. D1). If a random sample of 20 U.S. income earners aged 15 and older is selected, what is the probability that
a. All 20 have bank accounts?
b. No more than 15 have bank accounts?
c. More than 10 have bank accounts?
d. What assumptions did you have to make to answer (a) through (c)?