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The population of a country doubled every 10 years from 1985 to 2015

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Bunuel
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The population of a country doubled every 10 years from 1985 to 2015 [#permalink] New post   26 Jan 2022, 04:15
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The population of a country doubled every 10 years from 1985 to 2015, what was the percent increase in population during that time?

A. 200%
B. 400%
C. 500%
D. 700%
E. 800%
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desertEagle
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The population of a country doubled every 10 years from 1985 to 2015 [#permalink] New post   29 Jan 2022, 23:52
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Bunuel wrote:
Bunuel wrote:
The population of a country doubled every 10 years from 1985 to 2015, what was the percent increase in population during that time?

A. 200%
B. 400%
C. 500%
D. 700%
E. 800%



Bumping for discussion. Destroy this one and get Kudos for a correct solution!!!!



1985 to 2015 = 3 decades

Population doubles every decade. So, final population will be \(2^3=8\) times of original population.
Let initial population be P. Then final poulation will be 8P.
Percentage increase = \(\frac{(8-1)P}{P}\) x 100 = 700%
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Re: The population of a country doubled every 10 years from 1985 to 2015 [#permalink] New post   01 Feb 2022, 21:41
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1985=x
1995=2x
2005=4x
2015=8x

(8x-x)/x *100=700%
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parth04red
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Re: The population of a country doubled every 10 years from 1985 to 2015 [#permalink] New post   02 Feb 2022, 00:16
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Bunuel wrote:
The population of a country doubled every 10 years from 1985 to 2015, what was the percent increase in population during that time?

A. 200%
B. 400%
C. 500%
D. 700%
E. 800%


Let initial population = I
The population doubles every decade, and time given is 3 decades.
The population increases at the rate of 2^n
n = 3
Hence, population after 3 decades will be 2^3 = 8 times the initial population = 8I
% increase = {(8I - I)/I} * 100
This gives a 700% increase in population.
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The population of a country doubled every 10 years from 1985 to 2015 [#permalink] New post   28 Jan 2022, 18:03
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Lets first find how many years are between 2015 and 1985:

2015-1985 = 30

Therefore the population doubled 3 times.

Plug in a number for the population. Lets use 2.

==> 2*2*2*2 = 16

We can easily see 16 is 800% larger than 2.

Or calculate it:

x% of 2 = 16
x/100 * 2 = 16
x= 800

==> E
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The population of a country doubled every 10 years from 1985 to 2015 [#permalink]
28 Jan 2022, 18:03
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