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Bacteria Quadruples

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by neeti2711 » Tue Mar 05, 2013 3:05 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) 4:00 a.m.
(B) 5:00 a.m.
(C) 6:00 a.m.
(D) 7:00 a.m.
(E) 9:00 a.m.
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by guerrero » Tue Mar 05, 2013 3:15 am
neeti2711 wrote: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?
from 1/8th full to half 1/2 full culture of bacteria should quadruple - i.e 1/8*4=1/2,
Given that it quadruples every hour then container was one-eighth full at 10:00 a.m -1 hour

9 Am OA
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by Anurag@Gurome » Tue Mar 05, 2013 3:46 am
Refer to the post here >> https://www.beatthegmat.com/problem3-t152589.html#543949
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by GMATGuruNY » Tue Mar 05, 2013 4:00 am
neeti2711 wrote: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) 4:00 a.m.
(B) 5:00 a.m.
(C) 6:00 a.m.
(D) 7:00 a.m.
(E) 9:00 a.m.
Let the full container = 8 bacteria.
Since the container is half full at 10am, the number of bacteria at 10am = (1/2)8 = 4.
When the container is one-eighth full, the number of bacteria = (1/8)8 = 1.
Since the culture quadruples every hour, it takes one hour for the number of bacteria to increase from 1 to 4, implying that the container was one-eighth full at 9am.

The correct answer is E.
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