A department store analyzed its most recent sales and determined the relationship between the way the customer paid for the item and the price category of the item. The joint probabilities in the following table were calculated.

a. What proportion of purchases was paid by debit card?
b. Find the probability that a credit card purchase was more than $100.
c. Determine the proportion of purchases made by credit card or by debitcard.

Cash Credit Card Debit Card Less than $20 09 03 $20-$100 More than S100 03 23 .04 18 14 05 21