Food express is running a special promotion in which customers can win a free gallon of milk with their food purchase if there is a star on their receipt. so far, 219 of the first 264 customers have not received a star on their receipts. what is the experimental probability of winning a free gallon of milk?

In this case probability is the likelihood that from 264 customers one customer wins free gallon of milk with his food purchase, or in other words the probability that one customer receives a star on his receipt.
Probability is the ratio of the number of favorable outcomes to the total number of all  possible events. From 264 customers, 219 have not received a star. The opposite is to receive a star and that is the situation: (1-219)/264=0.17,

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.