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Boats & Streams, Pipes & Cisterns · Question 18 of 85

How long would the ferry take to cover the same 24 km across a still lake?

Question 18

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.

How long would the ferry take to cover the same 24 km across a still lake?

Options for question 18

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. In still water it moves at 10 km/h.

  2. 2410=2.4\frac{24}{10} = 2.4 hours, that is 144 minutes.

Worth noting

150 minutes averages the two trip times, 2 and 3 hours; it is the speeds that average.

Concept
The still-water time
Typical time
120 s
Your time
—
The rule this testsUpstream and downstream speeds
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Ten questions from Boats & Streams, Pipes & Cisterns, at your own pace.

Practise this chapter →

Ten questions from Boats & Streams, Pipes & Cisterns, at your own pace.

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