It is known that 70% of the customers in a sporting goods store purchase a pair of running shoes. Assume that customers' purchases are made independently, and let x represent the number of customers who purchase running shoes. a) In a random sample of 10 customers, find the probability that exactly 8 customers purchase running shoes. b) In a random sample of 100 customers, use normal approximation to find the probability that at least 61 customers purchase running shoes. [Use continuity Correction]