Problem-Solving and Data AnalysisVery hardNet change after a fall and a rise
Problem-Solving and Data Analysis practice question
A town's population fell by 20% between 2010 and 2020 and then rose by 25% between 2020 and 2030. By what percent did the population change between 2010 and 2030?
Answer: 0
0.8 × 1.25 = 1.00, so the population ended where it started: a 0% change.
Common wrong answers
- If you answered 5
- 5% adds the two percentages, ignoring that they apply to different bases.
- If you answered 45
- 45% treats the changes as 20% and 25% of the original added together.
- If you answered -5
- −5% subtracts them the other way.
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