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kaplan #14

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kaplan #14

by magical cook » Wed Aug 22, 2007 5:15 pm
14) Steve gets on the elevator at the 11th floor of a building and rides up at a rate of 57 floors per minutes. At the same time Joyce gets on an elevator on the 51st floor of the same building and ridses down at a rate of 63 floors per minutes. If they continue traveling at these rates. at which floor will their paths cross?

19
28
30
32
44

Can anyone help pls? Correct answer will follow.
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by ratindasgupta » Wed Aug 22, 2007 10:14 pm
when two objects are going in the opposite direction, the speed is the sum of their individual speeds = 57 + 63 = 120 flrs per minute.

time the two take to pass each other is (total distance)/(total speed).

Total distance is 51 - 11 = 40 floors.

So 40/120 = 1/3 minute = 20 seconds

So if steve travels at 57 floors a minute, in 20 seconds he'll travel 19 floors. So they will cross each other at the 30th floor.
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