Problem-Solving and Data AnalysisHardCapacity from a change in percent full
Problem-Solving and Data Analysis practice question
A water tank is 40% full. After 150 litres are added, it is 70% full. What is the capacity of the tank, in litres?
Answer: 500
The 150 litres raised the level from 40% to 70%, a change of 30% of the capacity. So 0.30 × capacity = 150, and the capacity is 150 / 0.30 = 500.
Common wrong answers
- If you answered 45
- 45 is 150 × 0.30, multiplying instead of dividing.
- If you answered 214
- 214 is about 150 / 0.70, treating the 150 litres as 70% of the tank. It is the 30% difference that equals 150.
- If you answered 375
- 375 is 150 / 0.40, treating 150 as 40% of the tank.
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