ACT Preparation / Unit 7 ACT 0621 worked example, 60 to 90 seconds
Finding and Comparing Unit Rates
The idea
To compare two rates, work in three steps. First, write each as a fraction with the same quantity on top in both: cost over ounces, or miles over gallons. Second, divide to get each unit rate. Third, compare the unit rates, deciding first whether the better one is higher or lower: a lower price per ounce is better, and more miles per gallon is better.
In practice
Worked example: a 12-ounce box of cereal costs $3.60, and a 20-ounce box costs $5.40. Unit prices: 3.60 ÷ 12 = 0.30, or 30 cents an ounce; 5.40 ÷ 20 = 0.27, or 27 cents an ounce. The 20-ounce box is the better buy, by 3 cents an ounce.
Where people slip
Divide in one consistent direction. Ounces per dollar would also work, but then the higher number wins, and mixing the two directions reverses the answer.
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