AlgebraVery hardWhen two tanks hold the same amount
Algebra practice question
Tank A holds 500 litres and is draining at 20 litres per minute. Tank B holds 200 litres and is filling at 10 litres per minute. After how many minutes will the two tanks hold the same amount?
Answer: 10
500 − 20t = 200 + 10t gives 300 = 30t, so t = 10.
Common wrong answers
- If you answered 15
- 15 solves 500 − 20t = 200, ignoring tank B's filling.
- If you answered 30
- 30 solves 300 = 10t.
- If you answered 300
- 300 is the difference in litres, not the time.
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