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AlgebraMediumTime at which a rising temperature reaches a value

Algebra practice question

The temperature in a greenhouse rises at a constant rate from 15°C at 6 am to 24°C at 9 am. How many hours after 6 am does the temperature reach 21°C?

Answer: 2

The rate is 3°C per hour, and 21 − 15 = 6, so 6/3 = 2 hours.

Common wrong answers

If you answered 3
3 is when it reaches 24°C.
If you answered 7
7 divides 21 by 3.
If you answered 1.5
1.5 halves 3 without using the temperatures.

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