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:

Explanation

The second train travels 400 km in 4 hours:

v_2=400/4=100 km/hr.
The speed ratio is 7:8, so:

v_1=100×(7/8)=87.5 km/hr.