A man can walk up a moving-up escalator in 30 seconds. The same man can walk down the same moving-up escalator in 90 seconds. How long would it take him to walk up the escalator when it is not moving?
Show answer & explanation
Correct answer: A
Explanation
Given:
Upward time = 30 seconds
Downward time = 90 seconds
Formula:
Length of escalator = person's speed ± speed of escalator
Let the person's speed = p
Speed of escalator = e
Going up:
p + e = 1/30
Going down:
p − e = 1/90
Add both:
2p = 1/30 + 1/90
2p = (3 + 1) / 90
2p = 4/90
p = 2/90
p = 1/45
Time = 45 seconds