Walking at 60% of his usual speed, a man reaches his destination 1 hour 40 minutes late. His usual time (in hours) to reach the destination is:

Answer: Option B

$$60\%=\frac{3}{5}$$
Let the speed of the man be 5x
60% of the speed = 5x × $$\frac{3}{5}$$ = 3x
Ratio of speed of man before and after = 5x : 3x
As we know, speed is inversely proportional to time.
Time ratio of man before and after = 3x : 5x
According to the question
5x - 3x = 1 hr 40 min
5x - 3x = $$\left(1+\frac{40}{60}\right)\text{hr}$$
2x = $$\frac{5}{3}$$
x = $$\frac{5}{3\times 2}$$
x = $$\frac{5}{6}$$ hr
Required time = 3x = 3 × $$\frac{5}{6}$$ = $$2\frac{1}{2}$$ hr