A school boy walks from his house to school at the rate of 4 kmph. He reaches the school 20 minutes earlier than the schedule time. If he walks at the rate of 3 kmph, he reaches the school 20 minutes late. What is the distance of the school from his house?
12 km
480 km
21 km
8 km
Explanation:
$Distance= \dfrac{s_{1}\times s_{2}}{s_{1}-s_{2}}\times\dfrac{Difference in time}{60}$
$=\dfrac{4\times3}{1}\times\dfrac{40}{60}$
=$4\times3\times\dfrac{2}{3}$
=8km