If a student walks from his home to school at the speed of 3 km/hr, he gets late by 4 min and if he increases his speed by 2 km/hr, he reaches 4 min earlier. Find the distance between his home and school.

1 km

Distance is same, therefore speed is inversely proportional to time.

                  I               II

Speed          3     :      5

 Time          5      :      3   →   2 (Difference)

                                2   →   8 (4 mins early + 4 mins late) 

                                1   →   4 mins = \(\frac{4}{60}\) hr = \(\frac{1}{15}\) hr.

Therefore,  Distance =  speed × time = 5 × 3 × \(\frac{1}{15}\) = 1 Km