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Can any one explain me this ?

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Junior | Next Rank: 30 Posts
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by envyramana » Mon Jul 07, 2008 11:18 am
A certain culture of bacteria quadruples every hour. If a container with these bacteria was half full at 10:00 a.m., at what time was it one-eighth full?

(A) 9:00 a.m.
(B) 7:00 a.m.
(C) 6:00 a.m.
(D) 4:00 a.m.
(E) 2:00 a.m.

oa A
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by VP_Jim » Mon Jul 07, 2008 11:23 am
I think the easiest way to do this is to assign some values. Let's say that the whole container holds 800 bacteria. If it were half full at 10 am, there would be 400 bacteria in it at that time. Since they quadruple every hour, that means there were 100 bacteria in it at 9 am.

100 is 1/8 of 800, so that's the answer: 9 am.
Jim S. | GMAT Instructor | Veritas Prep
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by envyramana » Mon Jul 07, 2008 11:33 am
Can you explain with another example, as i am not able to understand the word quadraple in this context.
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by augusto » Mon Jul 07, 2008 11:49 am
Hi envyramana,

I hope I can help you with this.
A certain culture of bacteria quadruples every hour = Every hour the number of bacteria is multiplied by 4.

If a container with these bacteria was half full at 10:00 a.m. = at 10:00 the container was 1/2 full

at what time was it one-eighth full? At what time it was 1/8 full.

And the easy way to solve it (IMHO) is by dividing 1/2 by 4 until you reach 1/8, and each time you divide you have to substract one hour.

In this case (1/2) / 4 = 1/8, so the container was 1/8 full at 9:00 a.m.


Cheers,
Augusto
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by envyramana » Mon Jul 07, 2008 11:56 am
Thank you VP_Jim & augusto.

Ramana
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