Sonali has to cover a distance of 240 km. If she increased her speed by 10 km/hr, she takes 2 hours less time than the usual time. At the usual speed in how much time she will cover a distance of 80 km?

2 hrs 40 min

When the distance is same, ratio of speed and time are reciprocal 

Let the initila speed be (x) km/hr

Thus ratio of time will  (x + 10) : x 

Difference = 10R = 2

                      R = \(\frac{1}{5}\)

Distance = speed x time = (x) x (x + 10) x \(\frac{1}{5}\) = 240

                          x(x + 10) = 1200

   possible values of x = 30, 40

Initial speed = 30 km/hr

At this speed, time taken to cover 80km  =  \(\frac{distance}{speed}\) =  \(\frac{80}{30}\) = 2hr 40 min