The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 km in 4 hours, then the speed of the first train is:

Question: The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 km in 4 hours, then the speed of the first train is:
[A].

70 km/hr

[B].

75 km/hr

[C].

84 km/hr

[D].

87.5 km/hr

Answer: Option D

Explanation:

Let the speed of two trains be 7x and 8x km/hr.

Then, 8x =		400		= 100
		4

x =		100		= 12.5
		8

Speed of first train = (7 x 12.5) km/hr = 87.5 km/hr.