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Problem Solving

by rnaah » Thu Sep 29, 2011 7:07 am
When water is poured on "cuscus" (a special food stuff of the Arabs), it doubles its size in its container every minute. If it takes 30 minutes for this soaked cuscus to fill its container, in which minute will the container be 1/16th full?
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by Brent@GMATPrepNow » Thu Sep 29, 2011 7:10 am
rnaah wrote:When water is poured on "cuscus" (a special food stuff of the Arabs), it doubles its size in its container every minute. If it takes 30 minutes for this soaked cuscus to fill its container, in which minute will the container be 1/16th full?
Time : Fraction filled
30 minutes : 1 (full)
29 minutes : 1/2 full
28 minutes : 1/4 full
27 minutes : 1/8 full
26 minutes : 1/16 full

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by CappyAA » Thu Sep 29, 2011 7:13 am
You know the cuscus doubles in size every minute. So start at 30 minutes and work backwards.

At 30 minutes, the container is full. At 29 minutes, the container is 1/2 full. At 28 minutes, the container is 1/4 full. At 27 minutes, the container is 1/8 full. At 26 minutes, the container is 1/16 full.
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by rohit_gmat » Thu Sep 29, 2011 7:35 am
rnaah wrote:When water is poured on "cuscus" (a special food stuff of the Arabs), it doubles its size in its container every minute. If it takes 30 minutes for this soaked cuscus to fill its container, in which minute will the container be 1/16th full?
factor = 2 (double)
times = 30 (mins)

2^(30) => full container
(2^30))/(1/16) = 2^30/2^4 = 2^26

26 mins ...
but of course countin backwards is much easier n faster n clearer but i did it the other way :D
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