AlgebraHardSpeed of a current from a round trip
Algebra practice question
A boat travels 24 kilometres downstream in 2 hours and makes the return trip upstream in 3 hours. The boat's speed in still water and the current's speed are both constant. What is the speed of the current, in kilometres per hour?
Answer: 2
Downstream speed = 24/2 = 12 km/h = b + c; upstream = 24/3 = 8 km/h = b − c. Subtracting: 2c = 4, so c = 2 (and b = 10).
Common wrong answers
- If you answered 4
- 4 is 2c, the difference between the two speeds.
- If you answered 10
- 10 is the boat's speed in still water.
- If you answered 12
- 12 is the downstream speed.
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