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Percentages

by jayanti » Fri Aug 12, 2011 7:11 am
Enrollment in City College in 1980 was 83^1/3 percent of enrollment in 1990. What was the percent increase in the college's enrollment from 1980 to 1990?
A. 10%
B. 16^2/3%
C. 20%
D. 25%
E. 183^1/3%
Last edited by jayanti on Fri Aug 12, 2011 7:45 am, edited 1 time in total.
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by kmittal82 » Fri Aug 12, 2011 7:33 am
We are dealing in %, so lets pick a number to make life easier.

Enrollment in 1990 = 100
Enrollment in 1980 = 83

So, what percent does 83 need to be increased by to give 100 ?

83 + (x/100) * 83 = 100

solve to get x = 20 as the closest value.

So, (C) I think
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by jayanti » Fri Aug 12, 2011 7:49 am
Hi, have reedited the question, some how 1/3 did not show in the tag. Pls explain.
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by gmatboost » Fri Aug 12, 2011 7:54 am
You should immediately recognize that 83 1/3 % = 0.833333 = 5/6.
This is one of the common fractions you need to know.

So, the change was from 5/6 x to x.
The change was 1/6 x.
Since the original amount was 5/6 x, the % increase is:
(1/6)x / [(5/6)x] =
(1/6) / (5/6) =
(1/6) * (6/5) = 6/30 = 1/5 = 20%
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by jayanti » Fri Aug 12, 2011 8:12 am
Thanks a lot GMAT Boost, but could you pls tell what are the other percentage fractions one need to learn.
Thanks for your help.
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by GmatKiss » Sat Aug 13, 2011 5:35 am
awaiting response :)

TIA,
GK
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by gmatboost » Mon Aug 15, 2011 9:00 am
Thanks a lot GMAT Boost, but could you pls tell what are the other percentage fractions one need to learn.
Sorry for the delay, I decided to answer in the form of a blog post so that I could refer to it in the future:

https://blog.gmatboost.com/2011/08/15/me ... rcentages/

Let me know if you have any questions.
Greg Michnikov, Founder of GMAT Boost

GMAT Boost offers 250+ challenging GMAT Math practice questions, each with a thorough video explanation, and 100+ GMAT Math video tips, each 90 seconds or less.
It's a total of 20+ hours of expert instruction for an introductory price of just $10.
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