Problem-Solving and Data AnalysisVery hardAverage speed for a round trip
Problem-Solving and Data Analysis practice question
A cyclist rides 60 kilometres from home to a lake at an average speed of 30 kilometres per hour, then rides straight back along the same road at an average speed of 60 kilometres per hour. What is the cyclist's average speed, in kilometres per hour, for the whole round trip?
Answer: 40
Average speed is total distance over total time. Out: 60/30 = 2 hours. Back: 60/60 = 1 hour. Total: 120 km in 3 hours = 40 km/h.
Common wrong answers
- If you answered 30
- 30 is the outbound speed alone.
- If you answered 45
- 45 is the mean of 30 and 60. But the slower half of the trip takes longer, so it pulls the average down: 40, not 45.
- If you answered 90
- 90 adds the two speeds; speeds don't add across legs of a journey.
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