By walking at3of his usual speed, 4a man reaches his office

By walking at 3 of his usual speed,
4
a man reaches his office 20 minutes later than his usual time. The usual time taken by him to reach his office is

4	of usual time = Usual time + 20 minutes
3

∴	1	of usual time = 20 minutes
	3

⇒ Usual time = 20 × 3
= 60 minutes
Second Method :
Here, A = 3, B= 4, t = 20 minutes

Usual time taken =	A	× time
	Diff. of A and B

=	3	× 20 = 60 minutes
	(4 − 3)