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# Growth

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Manager
Joined: 04 Dec 2008
Posts: 106
Followers: 1

Kudos [?]: 86 [0], given: 2

Growth [#permalink]  16 Jul 2009, 01:41
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
The population of a bacteria culture doubles every 2 minutes. Approximately how many minutes will it take for the population to grow from 1,000 to 500,000 bacteria?

(A) 10
(B) 12
(C) 14
(D) 16
(E) 18

Is there a shortcut to growth questions? Thks.
Senior Manager
Joined: 23 Jun 2009
Posts: 354
Location: Turkey
Schools: UPenn, UMich, HKS, UCB, Chicago
Followers: 5

Kudos [?]: 98 [0], given: 63

Re: Growth [#permalink]  16 Jul 2009, 02:26
in min1=x becomes 2x
in min2= 2x becomes 4x
....
in minn=x.$$2^(n-1)$$ becomes x.$$2^n$$
x.$$2^n$$ / x = $$2^n$$
When we take the logarithmics of right side in base 2
log2($$2^n$$) we can find n
That is maths.
But in this question we can an easy approach.
500000/1000=500
it is greater than 256 (2^8) and it is less than 512 (2^9) so we can say that in 9 minutes bacteria can grow up to that size.
Senior Manager
Joined: 23 Jun 2009
Posts: 354
Location: Turkey
Schools: UPenn, UMich, HKS, UCB, Chicago
Followers: 5

Kudos [?]: 98 [0], given: 63

Re: Growth [#permalink]  16 Jul 2009, 11:58
Thanks walker 9x2 = 18 minutes
Re: Growth   [#permalink] 16 Jul 2009, 11:58
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