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:
70 km/hr
75 km/hr
84 km/hr
87.5 km/hr
Explanation:
Let the speed of two trains be 7$ x $ and 8$ x $ km/hr.
| Then, 8$ x $ =$ \left(\dfrac{400}{4} \right) $= 100 |
| $\Rightarrow x $ =$ \left(\dfrac{100}{8} \right) $= 12.5 |
$\therefore$ Speed of first train = $(7 \times 12.5)$ km/hr = 87.5 km/hr.