A train covers 400 km at a uniform speed. If the speed had been 10 km/h more, it would have taken 2 hours less for the same journey. What is the usual time taken (in hours) by it to complete the journey?

10

Let Usual Speed  = S km

According to question ,

\(\frac{400}{S}\) - \(\frac{400}{S + 10 }\) = 2

\(\frac{400(S+10)  - 400S}{S(S+10)}\) = 2

S(S+10) = 2000

on solving , S = 40 km/h

Time taken to cover 400km with usual speed ,

= \(\frac{400}{40}\) 

= 10 hours