as a promotion, the first 50 customers who entered a certain store at a mall were asked to choose from one of two discounts. the first discount choice was 20% off all purchases made that day. the second discount choice was 10% off all purchases for the week. of those who received the discounts, 28 chose the first discount and 22 chose the second discount. one customer will be selected at random from those who received a discount. let ff represent the event that the selected person chose the first discount, and let ss represent the event that the selected person chose the second discount. are ff and ss mutually exclusive events?