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Time, Speed & Distance · Question 58 of 71

Question 58

EasyOriginal question

A motorboat goes downstream at 18 km/h and upstream at 12 km/h. What is its speed in still water?

3 km/hCorrect answerYour answer6 km/hCorrect answerYour answer15 km/hCorrect answerYour answer30 km/hCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer C

Correct answer: C

Downstream = boat + stream; upstream = boat − stream.
Speed in still water $= \frac{18 + 12}{2} = 15$ km/h.

Worth noting

3 km/h is the speed of the stream, half the difference $18 - 12$ .

Concept: Still-water speed is the average of downstream and upstream speeds
Typical timeTypical: 30 s
Your timeYours: —

The rule this testsBoats and streams

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