AlgebraMediumCurrent speed from an upstream journey
Algebra practice question
A boat's speed in still water is 12 kilometres per hour. Travelling upstream against a steady current, the boat takes 5 hours to go 40 kilometres. What is the speed of the current, in kilometres per hour?
Answer: 4
Upstream speed = 40 ÷ 5 = 8 km/h = 12 − c, so c = 4.
Common wrong answers
- If you answered 8
- 8 is the upstream speed, not the current.
- If you answered 20
- 20 comes from 12 + 8, adding instead of subtracting.
- If you answered 2.4
- 2.4 comes from 12 ÷ 5.
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