The ratio between the speeds of two trains is 7: 8. If the second train runs 400 kms in 4 hours, then the speed of the first train is ?  Pick one:
A) 17.5 km/hr
B) 27.5 km/hr
C) 67.5 km/hr
D) 87.5 km/hr
E) 77.5 km/hr
Explanation:   Let the speeds of two trains be 7X and 8X km/hr.   8x = {\color{Blue} \frac{400}{4}}   =&gt; x= 12.5 km/hrX=4004=&gt;X=12.5Km/hr   So speed of first train is   12.5*7= 
<gadget id="calculator">  12.5*7</gadget>
<output>87.5</output>
87.5 km/hr   Answer: 87.5 km/hr
<result>D</result>
The ratio between the speeds of two trains is 7: 8. If the second train runs 400 kms in 4 hours, then the speed of the first train is ?