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