You may also use a ratio to compare the number of elephants to the total number of animals in a zoo, or the amount of calories per serving in two different brands of ice cream. Look at the unit prices...You may also use a ratio to compare the number of elephants to the total number of animals in a zoo, or the amount of calories per serving in two different brands of ice cream. Look at the unit prices—the container on the right is actually a better deal, since the price per ounce is lower than the unit price of the container on the left.