Question

By walking at $\frac{3}{4}$th of his usual speed, a man reaches office 20 minutes later than usual. What is his usual time?

• A. 30 min
• B. 60 min
• C. 70 min
• D. 50 min

Answer 1

The correct option is B

60 min

Suppose that the man travels at a speed $v$ and takes time $t$ minutes to reach his office.

When he travels at $\frac{3}{4}$th of his usual speed, new speed $=\frac{3v}{4}$

As per the question, $vt=\frac{3v}{4}\times (t+20)$

$\Rightarrow t=\frac{3t}{4}+15$

$\Rightarrow \frac{t}{4}=15$

$\therefore t=60minutes$