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AlgebraHardFunction from an initial value and a later value

Algebra practice question

A candle is 14 centimetres tall when lit and 2 centimetres tall after burning for 6 hours at a constant rate. Which function gives its height h, in centimetres, after t hours, for 0 ≤ t ≤ 7?

  1. A. h(t) = 14 − 2tCorrect
  2. B. h(t) = 14 − 6t
  3. C. h(t) = 2t + 2
  4. D. h(t) = 14 − t/2

Answer: A. h(t) = 14 − 2t

Rate: (14 − 2)/6 = 2 cm per hour. h = 14 − 2t.

Why the other answers are wrong

B. h(t) = 14 − 6t
−6t uses the number of hours as the rate.
C. h(t) = 2t + 2
2t + 2 grows instead of shrinking.
D. h(t) = 14 − t/2
t/2 would take 24 hours to burn 12 cm.

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