Multiple choice general knowledge math & puzzles

You walk upwards on an escalator, with a speed of 1 step per second.After 50 steps you are at the end.You turn around and run downwards with a speed of 5 steps per second.After 125 steps you are back at the beginning of the escalator.How many steps do you need if the escalator stands still?

  1. 100

  2. 99

  3. 98

  4. 101
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let escalator speed = e steps/sec. Upward: 50/(1+e) = time, so 50 = (1+e)t. Downward: 125 = (5-e)t. Solving gives t = 100/3 seconds and e = 1/2 steps/sec. Steps visible when still = 1 * 100/3 + (1/2)*(100/3) = 100/2 = 100 steps.

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