Question

A man hoes from a place A to B at a speed of 12km/hr and returns from B to A at a speed of 18 km/hr. The average speed for the whole journey of distance 12km is :

• A. $14\frac{2}{5}km/hr$
• B. $15\frac{1}{2}km/hr$
• C. $15km/hr$
• D. $16km/hr$

Answer 1

Answer: (A)

Distance $=12km$

Speed of man when he goes from A to B $=12kmph$

Time taken $=\frac{12}{12}=1hour$

Speed of man when he goes from B to A $=18kmph$

Time taken $=\frac{12}{18}=\frac{2}{3}hours$

Total Distance $=12\times 2=24km$

Total time $=1+\frac{2}{3}=\frac{5}{3}$

Average speed $=\frac{24}{5/3}$

$=\frac{24\times 3}{5}$

$=\frac{72}{5}$

$=14\frac{2}{5}kmph$