AlgebraMediumCapacity from two fractional fill levels
Algebra practice question
A tank is two fifths full. After 36 litres are added, it is seven tenths full. What is the capacity of the tank, in litres?
Answer: 120
(7/10 − 2/5)C = 36 → (7/10 − 4/10)C = (3/10)C = 36 → C = 120.
Common wrong answers
- If you answered 48
- 48 is the volume in the tank before the 36 litres were added (2/5 of 120).
- If you answered 90
- 90 comes from (2/5)C = 36, treating the 36 litres as the original contents.
- If you answered 51.4
- 51.4 comes from (7/10)C = 36.
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