Question

When a man stands on a moving escalator he goes up in $40s$ and when he walked up the moving escalator he goes up in $20s$. The man walk up the stationary escalator in a time of:

• A. $60s$
• B. $40s$
• C. $20s$
• D. $50s$

Answer 1

The correct option is B $40s$

Let 'D' be the distance traveled by a man with respect to earth, 'S' be the speed of escalator and 'x' be the speed of man with respect to earth.

$D=S\times t$

$D=S\times \mathrm{40....................}\left(i\right)$

Man add his speed with escalator and reach in 20sec.

$D=(S+x)\times \mathrm{20...........}\left(ii\right)$

Putting value of S from (i) to (ii)

$D=(\frac{D}{40}+x)\times 20=\frac{1}{2}D+20x$

$\frac{1}{2}D=20x$

$\frac{D}{x}=20\times 2=40sec$