A company is studying the number of daily debit card purchases. if there were 20 purchases and the probability of a debit card purchase is 0.5. a) Of the 20 purchases, what is the expected value of the number of debit card purchases? b) What is the standard deviation of the number of debit card purchases? C) What is the probability that exactly 5 purchases were made by debit cards? D) Based on the shape of the distribution, approximately 99.7% of the purchases should be between which two values?