Two friends hit the accelerator of their respective cars at the same time. Both of them have the same amount of petrol in their respective cars at the time they start. One can drive for 4 hours and the other can drive for 5 hours.

After driving for a while, they analyse that the amount of petrol left in one of their cars is 4 times that of the petrol left in other car.

Can you calculate how long they have been driving their respective cars ?

3.75

This question can be solved mathematically.

Let us assume that the initial amount of petrol is p.

The time for which they drove be t.

Now, the amount of petrol used by one car in t hours will be = pt / 4

The amount of petrol used by the second car in t hours will be = pt / 5

Now, the petrol left in the first car will be = (p - pt / 4)

The petrol left in the second car will be = (p - pt / 5)

According to the question

P - pt / 5 = 4(p - pt / 4)

T = 15 / 4 or 3.75 hours.

Therefore, both of the friends have driven the car for 3.75 hours.