(c) The probability that fewer than 75 of the 200 customers on a given day make a payment with a credit card. The probability of a customer using a credit card is 0.4
mean = np = 200 x 0.4 = 80 customers
standard deviation = 6.92
We want to find where 75 customers fits into this curve, and what percentage of customers will fit into this area.
Find the z score: z = (mean - x)/s = (80 75)/6.92 = 0.7225 which is 72.25%
The probability that fewer than 75 or less customers will pay by credit card is
0.7225 or 72.3%