The escalator
Algebra
Level
2
A person takes 30 seconds to walk up a stalled escalator. When standing on the same escalator, now moving, he is carried up in 20 seconds. How much time, in seconds, would it take him to walk up the moving escalator?
The answer is 12.
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1 solution
Let x be the distance traveled by the person. So using speed = distance / time, he has a speed of x/30 if he is walking on a stalled escalator and a speed of x/20 if he is standing on a moving escalator. So if he is walking in a moving escalator (assuming same direction), his speed would be the sum of his speed when walking in a stalled escalator and his speed when he is standing on a moving escalator,
total speed = x/30 + x/20 = x/12
time = distance / total speed = x / (x/12) = 12 seconds