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Time, Speed & Distance · Question 11 of 71

Question 11

MediumOriginal question

If Gurpreet walks to school at 4 km/h she is 10 minutes late, but at 5 km/h she is 5 minutes early. How far is her school?

2.5 kmCorrect answerYour answer4 kmCorrect answerYour answer5 kmCorrect answerYour answer7.5 kmCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer C

Correct answer: C

The two times differ by $10 + 5 = 15$ minutes $= \frac{1}{4}$ h.
$\frac{d}{4} - \frac{d}{5} = \frac{1}{4}$ , so $\frac{d}{20} = \frac{1}{4}$ .
$d = 5$ km.

Worth noting

Late and early are on opposite sides of the right time, so the gap is $10 + 5$ minutes, not $10 - 5$ .

Concept: Late-and-early problems: difference in travel times at two speeds
Typical timeTypical: 75 s
Your timeYours: —

The rule this testsSpeed, conversion and average speed

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