Question

A lady reaches her office 20 mins late by travelling at a speed of 20 km/h and reaches 15 mins early by travelling at a speed of 30 km/h. By how much time(early or late) will she reach her office if she travels at 25 km/h?

Answer 1

Travelling at `25` km/hr she will reach `1` mt early.

Explanation:

Let the distance of the office be `x` Km
Time taken at `20` km/hr is `x/20` hr; reaches `20/60=1/3`hr=20mt late
Time taken at `30` km/hr is `x/30` hr; reaches `15/60=1/4`hr=15mt early
Therefore `x/20-x/30=1/3+1/4 or x/60=7/12 or x=7/12*60=35`Km
Time taken at `30` km/hr is `35/30=35/30*60 =70`mt
Time taken at `25` km/hr is `35/25 =7/5 hr=7/5*60=84 mt`;
So travelling at `25` km/hr she will reach `70+15-84 =1`mt early.[Ans]