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AlgebraHardWhere a linear model reaches a target

Algebra practice question

A hiker starts a descent at an elevation of 1,200 metres and descends at a steady 150 metres per hour. After how many hours will the hiker be at an elevation of 300 metres?

Answer: 6

Elevation after t hours: 1,200 − 150t. Set it to 300: 1,200 − 150t = 300, so 150t = 900 and t = 6.

Common wrong answers

If you answered 2
2 is 300 / 150, treating the target as the distance descended. The distance descended is 1,200 − 300 = 900.
If you answered 8
8 is 1,200 / 150, the time to reach elevation ZERO. The target is 300 metres, which comes sooner.
If you answered 10
10 is (1,200 + 300) / 150, adding the target instead of subtracting it.

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