Multiple choice general knowledge math & puzzles

David gets on the elevator at the 11th floor of a building and rides up at the rate of 57 floors per minute. At the same time, Albert gets on an elevator at the 51st floor of the same building and rides down at the rate of 63 floors per minute. If they continue travelling at these rates, then at which floor will their paths cross ?

  1. 19

  2. 28

  3. 30

  4. 37
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The relative speed is 57 + 63 = 120 floors per minute. The distance between them is 51 - 11 = 40 floors. Time to meet = 40/120 = 1/3 minute. In 1/3 minute, David ascends 57 * (1/3) = 19 floors. Meeting floor = 11 + 19 = 30. Albert also descends 63 * (1/3) = 21 floors to reach 51 - 21 = 30.

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