Question

Hariram travels at a speed of $20kmh{r}^{-1}$ while going to school. While coming back, he travels at a speed of $30kmh{r}^{-1}$(due to less traffic). What is his average speed?

• A. $25kmh{r}^{-1}$
• B. $26kmh{r}^{-1}$
• C. $20kmh{r}^{-1}$
• D. $24kmh{r}^{-1}$

Answer 1

The correct option is D $24kmh{r}^{-1}$

Let the distance covered be D and the time taken $t_1$ while going from home to school and $t_2$ time taken while coming back.

From Home to school
Speed $=\frac{D}{t_1}=20$
So, $T_1=\frac{D}{20}$
And Similarly Returning back
Speed $=\frac{D}{t_2}=30$
So, $T_2=\frac{D}{30}$
$T_1+T_2=\frac{D}{20}+\frac{D}{30}$
Average Speed $=\frac{TotalDistance}{TotalTime}$
Total Distance $=D+D$
Total Time $=T_1+T_2$
Average Speed $=\frac{2D}{\frac{D}{20}+\frac{D}{30}}=\frac{2D}{\frac{5D}{60}}$
$=\frac{120}{5}=24km{h}^{-1}$