ACT Preparation / Unit 19 ACT 1819 worked example, 60 to 90 seconds
Quick Arithmetic From Data
The idea
Arithmetic from data is done in three steps. First, read the needed values with their units. Second, decide the operation the question asks for: a difference for how much more, a ratio for how many times, and a percent change for how much it grew or fell relative to where it started. Third, round to friendly numbers, compute, and compare with the choices.
In practice
Worked example: an invented study counts 240 frogs at a pond in 2010 and 180 in 2020. How many fewer? 240 − 180 = 60. By what percent did the count fall? 60 out of the original 240 is one quarter, 25%. How many times larger was the 2010 count? 240 ÷ 180 = 4/3, about 1.3 times.
Where people slip
Percent change divides by the starting value: 60 ÷ 180 would give about 33%, the wrong base.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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