Question

To travel 600 km, train A takes 2 hours more than train B. If the speed of train B is doubled, then, train B takes 4 hours less than train A. The speed (in km/hr) of train A and train B, respectively?

• A. (50, 40)
• B. (100, 150)
• C. (40, 60)
• D. None of these

Answer 1

Answer:

B. (100, 150)

Solution: Given: Total distance to travel = 600 km Formula used: Distance = Speed × Time Calculation: The speed of train A and train B is x km/hr and y km/hr, respectively. Case I: ⇒ 600/x - 600/y = 2 ---(1) Case II: ⇒ 600/x - 600/2y = 4 ---(2) Subtract both equations ⇒ -600/y + 600/2y = -2 ⇒ -(600/2y) = -2 ⇒ 300/y = 2 ⇒ y = 150 km/hr Put the value of y in equation (1), we have - ⇒ 600/x - 600/150 = 2 ⇒ 600/x = 2 + 4 ⇒ x = 600/6 ⇒ x = 100 km/hr ∴ The speed of train A and B is 100 km/hr and 150 km/hr respectively.