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Boats & Streams, Pipes & Cisterns · Question 19 of 85

What is the ferry's speed in still water?

Question 19

MediumOriginal question

A ferry runs between two jetties 24 km apart on a river. It makes the trip downstream in 2 hours and the trip back upstream in 3 hours.

What is the ferry's speed in still water?

9.6 km/hCorrect answerYour answer10 km/hCorrect answerYour answer11 km/hCorrect answerYour answer12 km/hCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer B

Correct answer: B

Downstream 12 km/h and upstream $\frac{24}{3} = 8$ km/h.
Still water $= \frac{12 + 8}{2} = 10$ km/h.

Worth noting

9.6 km/h is the round trip's average speed, 48 km in 5 hours.

Concept: Speed in still water from the two speeds
Typical timeTypical: 120 s
Your timeYours: —

The rule this testsUpstream and downstream speeds

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