A jogger desires to run a certain course in 1/4 less time than she usually takes. By what percent must she increase her average running speed to accomplish this goal?
Let the jogger usually takes t minutes to cover a distance of x m.
So, his usual speed is x/t m/s.
Since, he desires to take 1/4 less time than he takes usually so, he desires to take 3t/4 minutes to cover x m.
In this case his speed has to be x/(3t/4) = 4x/3t m/s.
The speed that has to increase to desired the Jogger's goal = (4x/3t - x/t) m/s = x/3t m/s.
So, the percentage of speed the Jogger needs to increase = increase speed/original speed × 100 = 1/3 × 100 = 33.33 % (approx)