The ratio between the speeds of two trains is 5: 7. If the second train runs 840 kms in 6 hours, then the speed of the first train is ?  Pick one: A) 90 km/hr B) 120 km/hr C) 100 km/hr D) 110 km/hr E) None of these
Explanation:   Let the speeds of two trains be 5X and 7X km/hr.   7/X=840/6=&gt;X=20Km/hr   So speed of first train is   20*5= 
<gadget id="calculator">  20*5</gadget>
<output>100</output>
100 km/hr   Option 100 km/hr
<result>C</result>
The ratio between the speeds of two trains is 5: 7. If the second train runs 840 kms in 6 hours, then the speed of the first train is ?