A boat moves at 9 km/h in still water in a stream of 3 km/h. What is the ratio of the time it takes to go a distance upstream to the time to go it downstream?

1 : 2Correct answerYour answer2 : 1Correct answerYour answer3 : 1Correct answerYour answer4 : 3Correct answerYour answer

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CorrectNot quiteAnswer B

Correct answer: B

Upstream 6 km/h, downstream 12 km/h. For a fixed distance, time is inversely proportional to speed.
Time up : time down $= 12 : 6 = 2 : 1$ .

Worth noting

$1 : 2$ is the ratio of the speeds, upstream to downstream; times go the other way.

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

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

Explanation