A medium question on boats and currents for P5–P6, with a step-by-step solution, diagrams and the answer. Boats going with and against the current appear in the Hua Xia Cup's P5 and P6 first rounds, qualifying rounds and finals.
The question
A cruise boat runs between piers A and B, 70 km apart, with A upstream.
Downstream from A to B takes 5 hours; back upstream from B to A takes 7 hours.
The boat's still-water speed and the current both stay the same.
How fast does the boat go in still water, in km an hour?
Show the hints (2)
💡Hint 1: First find how many km an hour the boat makes downstream and upstream.
💡Hint 2: Downstream = boat + current; upstream = boat − current. How many currents apart are they?
Worked solution
Have a go first, then read the solution step by step.
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