Difference between revisions of "2012 AMC 10B Problems/Problem 13"
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Revision as of 09:13, 17 August 2017
Problem
It takes Clea 60 seconds to walk down an escalator when it is not operating, and only 24 seconds to walk down the escalator when it is operating. How many seconds does it take Clea to ride down the operating escalator when she just stands on it?
Solution 1
Let be the speed of the escalator and
be the speed of Clea. Using
, the first statement can be translated to the equation
. The second statement can be translated to
. Since the same distance is being covered in each scenario, we can set the two equations equal and solve for
. We find that
. The problem asks for the time it takes her to ride down the escalator when she just stands on it. Since
and
, we have
seconds. Answer choice
is correct.
P.R.A.N.K.E.D
Solution 2
Let
be the speed of the escalator and
be the speed of Clea. Then without loss of generality, assume that the length of the escalator be 1. Then
and
, so
. Thus the time it takes for Clea to ride down the operating escalator when she just stands on it is
.
See Also
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.
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