If a boy walks from his house to school at the rate of 4

If a boy walks from his house to school at the rate of 4 km per hour, he reaches the school 10 minutes earlier than the scheduled time. However, if he walks at the rate of 3 km per hour, he reaches 10 minutes late. Find the distance of his school from his house.

Let the distance of school be x km, then

x	−	x	=	20
3	−	4	=	60

⇒	x	=	1	⇒ x =	12	= 4 km
	12		3		3

Second Methdod :
Here, S₁ = 3, t₁ = 10
S₂ = 4, t₂ = 10

Distance =	(S₁ ×S₂)(t₁ + t₂)
	S₂ −S₁

=	(3 × 4)(10 + 10)
	4 − 3

= 12 ×	20	= 4 km
	60