Question : If a man goes from place A to B at a speed of 12 km/hr and return at a speed of 18 km/hr, then the average speed for the whole journey is:
Option 1: $6 \mathrm{~km} / \mathrm{hr}$
Option 2: $30 \mathrm{~km} / \mathrm{hr}$
Option 3: $14 \frac{2}{5} \mathrm{~km} / \mathrm{hr}$
Option 4: $15 \mathrm{~km} / \mathrm{hr}$
Correct Answer: $14 \frac{2}{5} \mathrm{~km} / \mathrm{hr}$
Solution :
Given: A man goes from place A to B at a speed of 12 km/hr and returns at a speed of 18 km/hr.
We know that,
Average speed = $\frac{2\times12\times18}{12+18}$ = $\frac{2\times12\times18}{30}$ = $\frac{72}{5}$ = $14 \frac{2}{5}$
Hence, the correct answer is $14 \frac{2}{5} \mathrm{~km} / \mathrm{hr}$.
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