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?
Choose the correct answer
A) 70 km/hr  B) 75 km/hr  C) 84 km/hr  D) 87.5 km/hr  E) 90.5 km/hr
Let the speed of two trains be 7x and 8x km/hr.   Then, 8x = [ 400/4= 
<gadget id="calculator">400/4</gadget>
<output>100</output>
100   x= [100/8= 
<gadget id="calculator">100/8</gadget>
<output>25/2 = around 12.5</output>
12.5   Speed of first train= (7 x 12.5) km/hr = 87.5 km/hr.   Answer is 87.5 km/hr
<result>D</result>
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?