AlgebraHardSpeed needed on the second half of a trip
Algebra practice question
A cyclist rode 60 kilometres at an average speed of 20 kilometres per hour for the whole trip. For the first 30 kilometres her average speed was 15 kilometres per hour. What was her average speed, in kilometres per hour, for the last 30 kilometres?
Answer: 30
The whole trip took 3 hours and the first half took 2, so the second half took 1 hour: 30 km/h.
Common wrong answers
- If you answered 20
- 20 is the overall average.
- If you answered 25
- 25 averages 20 and 30 or guesses the mean of 15 and something; average speed is distance over time.
- If you answered 45
- 45 assumes the speeds average to 20 by 15 + x = 60.
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