An easy question on boats and currents for P5, 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 school study tour takes a river cruise.
In still water the boat goes 10 km an hour, and the river flows at 2 km an hour; both speeds stay the same.
The boat sails downstream from pier A to pier B, 24 km away.
How many hours does the trip take?
Show the hints (2)
💡Hint 1: Going downstream, the river pushes the boat along. How far does it really go each hour?
💡Hint 2: Each hour it really goes 10 + 2 km.
Worked solution
Have a go first, then read the solution step by step.
1.Downstream speed = 10 + 2 = 12 km/h.
2.24 ÷ 12 = 2 hours.
⚠️Common mistake: dividing by 10, forgetting the river is carrying the boat too.
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