A boy walks 800m in 20 minutes. Calculate his average speed in km per hour

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Mathematics WAEC 2004

A boy walks 800m in 20 minutes. Calculate his average speed in km per hour

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The correct answer is: A

Explanation

\(Average \hspace{1mm}speed = \frac{Distance}{Time\hspace{1mm} taken}\\
Distance = 800m = \frac{800}{1000}km = 0.8km\\
Time\hspace{1mm}taken = 20\hspace{1mm}minutes = \frac{20}{60}hr=\frac{1}{3}hr\\Average \hspace{1mm} speed = \left(0.8\div \frac{1}{3}\right)km/hr = (0.8\times3)km/hr\\=2.4km/hr\)
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