Arun drives a car and covers a certain distance in 6 hours at a speed of 50 kmph. By what percent should the speed of Arun's car be increased to cover the same distance in 4 hours?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 50%
The distance stays the same, so the new speed is the same distance covered in the shorter time; the increase is then compared with the old speed.
Distance covered in 6 hours at 50 km/h: \(50\times6=300\) km
Speed needed to cover it in 4 hours: new speed \(\displaystyle=\frac{300}{4}=75\) km/h
Rise of 25 km/h as a percentage of the old speed: increase \(\displaystyle=\frac{75-50}{50}\times100=50\%\)
Shortcut:
For a fixed distance, speed is inversely proportional to time: new speed : old speed \(=6:4=1.5:1\)
So the speed rises by half, that is 50%