Question

John usually reaches his office on time. He walks to the office from the nearest metro station. One day, John walks to the office, lost in thought, at 3/4th of his usual speed and reaches his office 20 minutes late. How long does he usually take to reach his office?

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

Answer 1

The correct option is B 60 minutes

Let:
Distance covered : $d$
Usual speed : $s$
Usual time (in $minutes$) : $t$

Distance is the product of speed and time.
$d=st\left(i\right)$

When the person walks at $\frac{3}{4}$ of his usual speed,
Speed is: $s_2=\frac{3}{4}s$
Time is: $t_2=t+20$
Again, applying distance formula:
$d=s_2{t}_2$
$d=\frac{3}{4}s(t+20)\left(ii\right)$

Equating equations (i) and (ii),
$\frac{3}{4}s(t+20))=st$
$\Rightarrow 3t+60=4t$
$\Rightarrow t=60\text{minutes}$