A bank installed an ATM. After several months of operation, a sample of 100 customers showed the following use of the ATM in a month.
Number of Times ATM Used / Frequency
0 / 25
1 / 30
2 /20
3 /10
4 /10
5 /5


a. What is the estimate of proportion of customers who do not use the ATM in a month?


b. Develop 95 percent confidence interval for this estimate. Can the bank be sure that at least 40% of customers will use the ATM?