Question

A man walks at the rate of $5km/hr$ for $6$hours and at $4km/hr$ for $12$hours. The average speed of the man is:

• A. $4$
• B. $4\frac{1}{2}$
• C. $4\frac{1}{3}$
• D. $4\frac{2}{3}$

Answer 1

The correct option is C $4\frac{1}{3}$

To find: Average speed of the man.

Speed $=\frac{Distance}{Time}$

$\Rightarrow$ Distance $=$Speed$\times$ Time

$S_1=v_1\times t_1$

$S_1=(5\times 6)$km $=30$km

$S_2=v_2\times t_2$

$S_2=(4\times 12)$km $=48$km

Average speed $=\frac{S_1+S_2}{t_1+t_2}$

$=\frac{(30+48)km}{(6+12)hrs}=\frac{78}{18}km/h$

Average speed $=4\frac{1}{3}$km/h.