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
Ka-lok is rowing on the Shing Mun River in Sha Tin.
In still water he rows 50 m a minute, and the river flows at 10 m a minute; both speeds stay the same.
He rows upstream, against the current, for 3 minutes.
How many metres upstream does he get?
Show the hints (2)
💡Hint 1: Going upstream, the river pushes the boat back. How far does it really go each minute?
💡Hint 2: Each minute it really goes 50 − 10 m.
Worked solution
Have a go first, then read the solution step by step.
1.Upstream speed = 50 − 10 = 40 m a minute.
2.40 × 3 = 120 m.
⚠️Common mistake: 50 × 3 = 150 m, forgetting the current pushes him back 10 m every minute.
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