AlgebraHardTank capacity from two fractions
Algebra practice question
A tank is one quarter full. After 30 litres of water are added, it is two thirds full. What is the capacity of the tank, in litres?
Answer: 72
(2/3 − 1/4)C = 30 gives (5/12)C = 30, so C = 72.
Common wrong answers
- If you answered 40
- 40 comes from a wrong difference of 3/4.
- If you answered 45
- 45 uses 2/3 alone.
- If you answered 120
- 120 uses 1/4 alone, as if the 30 litres filled a quarter of the tank.
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