A man completes a certain journey by a car. If he covered 40% of the distance at the speed of 20kmph. 30% of the distance at 15 kmph and the remaining of the distance at 30 kmph, his average speed is-

Question: A man completes a certain journey by a car. If he covered 40% of the distance at the speed of 20kmph. 30% of the distance at 15 kmph and the remaining of the distance at 30 kmph, his average speed is-

Solution:
Suppose, total distance = 100 km

He covered 40% of the distance at the speed of 20 kmph
His time taken = 40/20 = 2 hours

He covered 30% of the distance at 15 kmph
His time taken = 30/15 = 2 hours

He covered the remaining of the distance at 30 kmph
The remaining of the distance = 100% - (40 + 30)% = 30%
His time taken = 30/30 = 1 hour

∴ Average speed = Total distance/time
= 100/(2 + 2 + 1)
= 20 kmph