Solution #25: Subway Escalator

Let x be the unknown number of steps. When I ride the escalator, I cover x - 20 steps in 60 seconds. When my wife uses the escalator, she covers x - 16 steps in 72 seconds. The escalator therefore moves at a rate of 4 steps every 12 seconds or 20 steps in 60 seconds. Its total height is therefore the sum of these 20 steps and of the additional 20 steps I climb: a total of 40 steps.
Source: Berrondom, Marie
Categories: Rates, Reasoning
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