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

Explanation

The second train covers 400 km in 4 hours, so v₂ = 100 km/h. The speed ratio first:second is 7:8, hence v₁ = 100 × 7/8 = 87.5 km/h.