Answer:
a

b

Step-by-step explanation:
From the question we are told that
The proportion that has outstanding balance is p = 0.20
The sample size is n = 15
Given that the properties of the binomial distribution apply, for a randomly selected number(X) of credit card

Generally the probability of finding 4 customers in a sample of 15 who have "maxed out" their credit cards is mathematically represented as

=> 
Here C stand for combination
=>
Generally the probability that 4 or fewer customers in the sample will have balances at the limit of the credit card is mathematically represented as
![P(X \le 4) = [ ^{15}C_0 * (0.20)^0 * (1 - 0.20)^{15-0}]+[ ^{15}C_1 * (0.20)^1 * (1 - 0.20)^{15-1}]+\cdots+[ ^{15}C_4 * (0.20)^4 * (1 - 0.20)^{15-4}]](https://tex.z-dn.net/?f=P%28X%20%5Cle%204%29%20%3D%20%20%5B%20%5E%7B15%7DC_0%20%2A%20%280.20%29%5E0%20%2A%20%281%20-%200.20%29%5E%7B15-0%7D%5D%2B%5B%20%5E%7B15%7DC_1%20%2A%20%280.20%29%5E1%20%2A%20%281%20-%200.20%29%5E%7B15-1%7D%5D%2B%5Ccdots%2B%5B%20%5E%7B15%7DC_4%20%2A%20%280.20%29%5E4%20%2A%20%281%20-%200.20%29%5E%7B15-4%7D%5D)
=> 