Walking at 80% of his usual speed, a man is 10 mins late to his office. Find the usual time taken by hime to reach his office.

A. 20 minutes
B. 30 minutes
C. 40 minutes
D. 50 minutes

Let his
usual speed be x kmph
usual travel time be t hours
distance to office be d km d=xt d=(0.8x)*[t+(10/60)] xt=0.8xt+(2x/15) Solving,
t=40 minutes