A train covers 450 km at a uniform speed. If the speed has been 5 km/h more . it would have taken 1 hour less to cover the same distance. How much time will it take to cover 315 km at its usual speed ?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 7 h
Let the speed of the train be 's' km/hr
Time taken by the train to cover 450 km = 450/s hr.
If the speed of the train increased by 5 km/hr then time taken by the train reduce by 1 hour.
450/(s + 5) = 450/s - 1
450/s - 450/(s + 5) = 1
[450(s + 5 - s)]/[s(s + 5)} = 1
450 × 5 = s × (s + 5)
2250 = s(s + 5) = 45 × 50
On comparing we get,
s = 45 km/hr.
Time taken by the train to cover 315 km = 315/45 = 7 hours.