ACT Preparation / Unit 7 ACT 0629 worked example, 60 to 90 seconds
Percent Change, Step by Step
The idea
A percent-change problem is solved in three steps. First, identify the original amount, the value before the change, and the new amount. Second, find the change by subtracting. Third, divide the change by the original and convert to a percent, naming it an increase or a decrease by its direction. To find a new amount from a percent change instead, multiply the original by one plus the rate for an increase, or one minus the rate for a decrease.
In practice
Worked example: a town's population fell from 2,500 to 2,150. Change: 2,500 − 2,150 = 350. Divide by the original: 350 ÷ 2,500 = 0.14, a 14% decrease. Second: a $60 jacket is marked up 15%: 60 × 1.15 = $69.
Where people slip
The original is the earlier value, whichever is larger. In a decrease, the original is the bigger number; in an increase, the smaller.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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