The gross weekly sales at a certain used-car lot are normal with mean $18,800 and standard deviation $9000.
(a) What is the probability that next week's sales exceed $20,000?
(b) What is the probability that weekly sales will exceed $20,000 in each of the next 2 weeks?
(c) What is the probability that the total sales in the next 2 weeks exceed $40,000?
In parts (b) and (c) assume that the sales totals in different weeks are independent.