Question

A car moving on a straight road covers one
third of the distance with 20 km/hr and rest with
60 km/hr. The average speed of th car:
(A) 40 km/hr (B) 80 km/hr
(C) 50 km/hr (D) 36 km/hr​

Answer 1

Explanation:

Let the original distance be X

so, Distance covered with 20 km/hr speed = X/3

speed=distance/time

time=distance/speed

Time-Taken to cover X/3 distance = X/3/20 h

=> x/60

Distance covered with 60 km/hr speed = X-X/3

=> 2X/3

Time taken to cover 2X/3 distance= 2X/3/60 h

=> X/90 h

Total time taken to cover the distance= X/60+X/90 h

=>3x+2x/180 h

=>5x/180 h

We know that

$average \: speed \: = \frac{total \: distance}{total \:time}$

AVG. Speed = X/5x/180 Km/h

=>180X/5X km/hr

=>36 km/hr

Hope the solution helps!

Have an nice year ahead :-)