Question

A man travels $1^{st}$ $50$ km at $25$ km/hr, next $40$ km with $20$ km/hr and then $90$ km at $15$ km/hr, then find his average speed for the whole journey (in km/hr)

Answer 1

Let the man travels with given distance and speeds for three different time intervals $t_1,t_2,t_3$

$t_1=\frac{50}{25},t_2=\frac{40}{20},t_3=\frac{90}{15}$

We know, $Speed=\frac{Distance}{Time}$

Avg. Speed = $\frac{50+40+90}{\frac{50}{25}+\frac{40}{20}+\frac{90}{15}}$ = 18 km/hr