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AlgebraEasyInterpreting a function value

Algebra practice question

A cyclist's distance d, in kilometres, after t hours is given by d(t) = 15t. Which statement best interprets d(2) = 30?

  1. A. After 2 hours, the cyclist has travelled 30 kilometres.Correct
  2. B. After 30 hours, the cyclist has travelled 2 kilometres.
  3. C. The cyclist's speed is 30 kilometres per hour.
  4. D. The cyclist rode for 15 hours.

Answer: A. After 2 hours, the cyclist has travelled 30 kilometres.

The input is time and the output is distance: 2 hours gives 30 km.

Why the other answers are wrong

B. After 30 hours, the cyclist has travelled 2 kilometres.
Input and output are swapped.
C. The cyclist's speed is 30 kilometres per hour.
The speed is 15 km/h, the coefficient of t.
D. The cyclist rode for 15 hours.
15 is the speed, not a time.

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