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Question

Benny walks to school at an average speed of 4km/h everyday. One day,after walking a distance of 1km, he realized that his watch was slow. So he ran at a constant speed and managed to reach school just on time. Later, he calculated that if he had run at this speed right from the start of the journey, he would have reached school 5mins earlier. What was his running speed? 

 

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Answer

“Later, he calculated that if he had run at this speed right from the start of the journey, he would have reached school 5mins earlier.”

This means that had he run the 1km instead of walking, he would have been 5 minutes faster. 

1/4 = 0.15

He took 0.15 hours, or 15 minutes to walk 1km. If he had ran, it would have taken him 10 minutes (5 minutes less), or 1/6 of an hour. 

1 / (1/6) = 6

Thus his running speed was 6km/h

 

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