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# DS: bacteria population

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Director
Joined: 23 Sep 2007
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DS: bacteria population [#permalink]  19 Jul 2008, 14:42
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Warning: this question requires that you discard any previous knowledge of bacterial growth characteristics.

Wes works at a science lab that conducts experiments on bacteria. The population of the bacteria multiplies at a constant rate, and his job is to notate the population of a certain group of bacteria each hour. At 1 p.m. on a certain day, he noted that the population was 2,000 and then he left the lab. He returned in time to take a reading at 4 p.m., by which point the population had grown to 250,000. Now he has to fill in the missing data for 2 p.m. and 3 p.m. What was the population at 3 p.m.?
50,000
62,500
65,000
86,666
125,000
Senior Manager
Joined: 23 May 2006
Posts: 328
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Re: DS: bacteria population [#permalink]  19 Jul 2008, 15:32
This is a gemometric progression series.

use the formula and you can calcuate the constant term.

2000r^3 = 250,000
r = 5
so at 3 = 2000(5^2) = 50,000

IMO A
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Re: DS: bacteria population [#permalink]  21 Jul 2008, 04:03
agree with A. you can use the given #s to find out the proportional constant in the relationship (turns out to be 5), and then use that to find out what the pop. was @ 3
Re: DS: bacteria population   [#permalink] 21 Jul 2008, 04:03
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