A) 10 sec
B) 30 sec
C) 20 sec
D) 40 sec
Correct Answer: C
Solution :
[c] Let the person covers a distance x on escalator in time t. Velocity of escalator \[{{v}_{1}}=\frac{x}{30}\,m/\sec ,\] Velocity of person \[{{v}_{2}}=\frac{x}{60}\,m/\sec ;\] \[t=\frac{x}{{{v}_{1}}+{{v}_{2}}}=\frac{x}{\frac{x}{30}+\frac{x}{60}}=20\,\sec \]
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