Correct Answer - Option 4 : 20/7
Given:
The distance between Mumbai and Pune = 300 km
Usual speed of the car = 50 km/h
Formula Used:
Time = Distance/Speed
Increased Speed = [(100 + percentage increase in speed)/100] × usual speed
Calculation:
The usual time taken to complete the journey from Mumbai to Pune is given by:
300/50 = 6 hours
∵ The time taken to complete the journey should be reduced by 10 minutes,
The required time to complete the journey, with the increased speed is given by
6 - 10/60 = 35/6 hours
The increased speed = distance/reduced time
⇒ Increased speed = 300/(35/6) = 360/7 km/h
The percentage increase in speed is given by
{[(360/7) - 50]/50} × 100 = [(360 - 350)/7] × 2
⇒ [(360 - 350)/7] × 2 = 20/7 %
∴ The required percentage increase in the speed of the car is 20/7 %