Question

A vehicle after covering of a journey of
120 kms develops some trouble and later
travels at 1/4 of its original speed. As a
result of which it arrives 3 hours late than
its normal time. Then find the normal
speed of the vehicle.​

Answer 1

He proceeds at 4/5 S where S is his usual speed means 1/5 decrease in speed which will lead to 1/4 increase in time. Now the main difference comes in those 12km (30-18) and the change in difference of time = (45-36) min = 9 min

Thus,
1/4 * T = 9 min where T is the time required to cover the distance of (30 - 18) = 12 km
T = 36 min = 36/60 hours = 0.6 hours.

Speed of the car = 12/0.6 = 20 kmph