# What two numbers do you divide to get the probability?

## Mr. McGee is the manager of the washer and dryer department of an appliance store. He wants to estimate the probability that a customer who comes to his department will buy a washer or dryer. He collected the following data during one week: 177 customers came to his department, 88 purchased washers, 64 purchased dryers, and 69 did not make a purchase. Make a two-way table. What to numbers do I divide to get the probability that a customer will buy a washer or dryer? I just need to know the numbers that I divide and I can do the rest.

$\frac{108}{177}$
Note that $88 + 64 + 69 = 221 > 177$, so clearly some people bought both a washer and a dryer. To figure out how to get the probability, we first need to figure out how many people made a purchase.
This is fairly straightforward, since we know how many did not make a purchase. If 69 people didn't make a purchase, then $177 - 69 = 108$ people did make a purchase.
So our probability is the number of people who made a purchase divided by the total number of people. That is, $\frac{108}{177}$.