Joseph and Fatima cycle the same route to college. Joseph takes 40 minutes and Fatima takes 50 minutes. If Joseph rides at 15 km/h, what is Fatima's speed?

12 km/hCorrect answerYour answer13.5 km/hCorrect answerYour answer15 km/hCorrect answerYour answer18.75 km/hCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer A

Correct answer: A

Route length $= 15 \times \frac{40}{60} = 10$ km.
Fatima's speed $= \frac{10}{50/60} = 12$ km/h.

Worth noting

For a fixed distance, speed is inversely proportional to time. Scaling 15 by $\frac{50}{40}$ gives 18.75 km/h, which wrongly makes the slower rider faster.

Concept: For the same distance, speed varies inversely with time
Typical timeTypical: 40 s
Your timeYours: —

The rule this testsSpeed, conversion and average speed

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Ten questions from Time, Speed & Distance, at your own pace.

Joseph and Fatima cycle the same route to college. Joseph takes 40 minutes and Fatima takes 50 minutes. If Joseph rides at 15 km/h, what is Fatima's speed?

Explanation