Question

Car a leaves city c at 5pm and is driven at a speed of 40 kmph. two hours later another car leaves city c and is driven in same direction as car

a. in how much time car b be 9 km ahead of car a if the speed of car b is 60 kmph.

Answer 1

The distance covered by a in 2 hrs is :

40 × 2 = 80km

Let the distance to be covered by a at the time b catches up with a be x.

They take the same time to reach the meeting point.

b covers 80 + x

Time taken by a is :

x/40

Time taken by b is :

(x + 80) / 60

x /40 = (x + 80) / 60

60x = 40(x + 80)

60x = 40x + 3200

60x - 40x = 3200

20x = 3200

x = 3200/20

x = 160

The time taken for them to catch up is :

160/40 = 4hrs

The relative distance is 9 km

Relative speed is :

60 - 40 = 20km/h

Time = 9/20 hrs

9/20 × 60 = 27 minutes

The total time is 4hrs + 27mins = 4hrs 27 mins