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population doubling 1

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by Gurpinder » Thu Aug 05, 2010 2:17 pm
4 years from now, the population of bees will reach 1.6x10^8. if the population of the colony doubles every 2 years, what was the population 4 years ago?

please EXPLAIN how I should tackle such a question.
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by indiantiger » Thu Aug 05, 2010 4:28 pm
lets say that 4 years ago the population of bees was x

lets start 4 years ago and then the timeline would look like :

years: 1-----2----3-----4-----5----6-----7-----8
population:x-----2x---------4x--------8x------------16x

16x = 1.6 * 10^8
x = .1 * 10^8
x = 1*10^7 (Answer)
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by nox104 » Thu Aug 05, 2010 5:14 pm
You could use the exponential formula below too..

P = S.2^t/I where
P = Final population
S = Initial population
t = time period
I = interval = how often it doubles / triples etc.

In this problem, to find the population 8 years ago..
16 x 10^7 = S 2^ 8/2 => S = 1x10^7
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