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GMAT PREP - percentage change

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by aleph777 » Sun Feb 27, 2011 5:49 am
Ok, my last prep review for the day...

I'm including two problems here, both of which I got correct, but I was a little shaky on my theory.

Basically, I approached them thinking that, in order to determine the change, you need either the new and the old or the percent change from new to old. You don't actually need the values, though. Is this the appropriate concept to apply here?

Thank you!
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Source: — Data Sufficiency |
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by maihuna » Sun Feb 27, 2011 6:22 am
For Q1, assuming 100 is the pop in 70's, you know pop in 80's is 120 and that in 90's 1.30*120 = 156

so %tage increase over the period is 56.
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by Anurag@Gurome » Sun Feb 27, 2011 6:23 am
First One:

Statement 1: We have the population in 1970, but no relation of that with that of in 1980 or 1990.

Not sufficient

Statement 2: We have the relation of population in 1980 and 1990 with that in 1970 in terms of percentage. Hence, we can represent the population of 1980 and 1990 as some fraction of the population of 1970. And hence we can find the percentage change between them too.

Sufficient

The correct answer is B.
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by Anurag@Gurome » Sun Feb 27, 2011 6:26 am
Second One: Refer to this post : https://www.beatthegmat.com/marla-t72684.html#329150
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by ankurmit » Tue Mar 01, 2011 8:38 pm
Anurag@Gurome wrote:First One:

Statement 1: We have the population in 1970, but no relation of that with that of in 1980 or 1990.

Not sufficient

Statement 2: We have the relation of population in 1980 and 1990 with that in 1970 in terms of percentage. Hence, we can represent the population of 1980 and 1990 as some fraction of the population of 1970. And hence we can find the percentage change between them too.

Sufficient

The correct answer is B.
Anurag, can you help me to find out exect percentage change from 1980 to 1990.

I am bit confused.
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by manpsingh87 » Tue Mar 01, 2011 9:28 pm
The first question talks about the percent increase,

statement 1) gives data about the 1970 population, which is not sufficient to evaluate the percent increase because we don't know the population in the year 1980 and 1990.

statement 2) suppose population in 1970 is 100, so in 1980 it becomes 120, and in 1990 it becomes 130, so the percentage increase from 1980 to 1930 would be; {(130-120)/120}*100
= 100/12 = 8.33%;

Hence statement 2 alone is sufficient to answer the question..!!
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