AlgebraVery hardTime for two linear quantities to match
Algebra practice question
A candle 100 millimetres tall burns down 4 millimetres per hour. A second candle is 60 millimetres tall and burns down 1 millimetre per hour. After how many hours will the two candles be the same height?
Answer: 13.33 or 40/3
100 − 4t = 60 − t gives 40 = 3t, so t = 40/3.
Common wrong answers
- If you answered 8
- 8 solves 100 − 4t = 60 + t, with the second candle growing.
- If you answered 10
- 10 solves 100 − 4t = 60.
- If you answered 40
- 40 is the difference in starting heights.
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