Two cars A and B leave Delhi at 8:30 a.m. and at 9 a.m. for Shimla, respectively. They travel at the speeds of 40km/h and 50 km/h respectively. How many kilometres away from Delhi will the two cars be together?

Cars A and B leave Delhi at 8:30 a.m. and at 9 a.m. for Shimla, respectively so,

Distance traveled by car A in 30 min = speed $$\times times = 40 \times 1/2 = 20 km

(30 min = 30/60 hr = 1/2 hr)

Relative speed of car B = 50 - 40 = 10 km/hr

Time taken by car B to cover 20 km  = 20/10 = 2 hr 

(Time = distance/speed)

Distance covered in 2 hr = 50 \times 2 = 100 km

$$\therefore$$ 100 kilometers away from Delhi will the two cars be together.