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A certain culture of bacteria quadruples every hour. If a

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Director
Joined: 09 Oct 2005
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A certain culture of bacteria quadruples every hour. If a [#permalink]  17 Jan 2006, 02:48
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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
It seems to be very simple but I am stuck here
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IE IMBA 2010

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Statement says
Time Population
T X
T+1 4X

In other word if we assume
T+1 X
T X/4

10 AM = 1/2 Full
9 AM = 1/4*1/2 Full = 1/8 Full
Senior Manager
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9 :00 am

as (1/2)/4 = 1/8 whis is what is asked
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9:00 AM

Population in the beginning = x/8

Population now = x/2 i.e 4 times that of in the beginning. So one hour has passed.
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Pop at 10 am is x/2 and population at t is x/8
so how much has the population increased

(x/2)/(x/8)=4 times and 4 times increase happens in 1 hr so (10-1)=9
Director
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Good Job guys OA is A
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andy_gr8 wrote:
Pop at 10 am is x/2 and population at t is x/8
so how much has the population increased

(x/2)/(x/8)=4 times and 4 times increase happens in 1 hr so (10-1)=9

very clear explanation. thanks

now / previous level

(x/2) / (x/8)
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