[EX03-008] Consider the accompanying contingency table, which presents the results of an advertising survey about the use of credit by Martan Oil Company customers.

Number of Purchases at Gasoline Station Last Year Preferred Method of Payment 0–4 5–9 10–14 15–19 20 Sum Cash 150 100 25 0 0 275 Oil-Company Card 50 35 115 80 70 350 National or Bank 50 60 65 45 5 225 Credit Card Sum 250 195 205 125 75 850

a. How many customers were surveyed?

b. Why are these bivariate data? What type of variable is each one?

c. How many customers preferred to use an oilcompany credit card?

d. How many customers made 20 or more purchases last year?

e. How many customers preferred to use an oilcompany credit card and made between five and nine purchases last year?

f. What does the 80 in the fourth cell in the second row mean?