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Quick method to calculate population few years ago

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Quick method to calculate population few years ago

by melguy » Mon Jun 17, 2013 4:30 am
Hello

Please help me with a quick method of calculating population n years ago (p / [1 + (X/100) ]n)

p (population now) = 20000
x % per annum = 20
n = 10 years

(200 / [1 - 20 /100 ]^ 10 )

This will be very time consuming so plz suggest a quicker way. Should I just take the number (20,000) and keep multiplying by 0.80 ten times? thanks
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by Brent@GMATPrepNow » Mon Jun 17, 2013 6:16 am
An official GMAT question would never require you to evaluate something like 200/[1 - 20/100]^10
Either the answer choices would look something like this:
A) 200/[1 - 20/100 ]^10
B) 200/[1 - 10/100 ]^20
C) 10/[1 - 20/100 ]^200
etc.

Or the question would feature an exponent much less than 10, like perhaps 2 (maybe 3), as in 200/[1 - 20/100 ]^2

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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