In a computer store, 30% (.3) of the computers in stock are laptops and 70% (.7) are desktops. Five percent (.05) of the laptops are on sale, while 10% (.1) of the desktops are on sale. Use a tree diagram to determine the percentage of the computers in the store that are on sale.

In an Italian breakfast café, a waitress has observed that 80% of her customers order coffee and 25% of her customers order both biscotti and coffee. Define

A = a randomly selected customer orders coffee.

B = a randomly selected customer orders biscotti.

a. Express the waitress’s observations as probability statements involving events A and B.

b. What is the conditional probability that a randomly selected customer would order a biscotti, given that he or she orders coffee?

c. What is the conditional probability that a customer would not order a biscotti, given that he or she orders coffee?