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Estimate Ansawer

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by jawad » Sun Jul 20, 2008 2:52 am
Hi ,
I have just started preparing for GMAT from PR Manual. There is this topic of " estimating Percent" for estimating ansawer when u get stuck on weird fraction. I do not understand logic to use for doing an estimation .

E.g to find an ansawer to 21120/64000 , PR has rounded off 21120 to 20,000 and 64000 to 60,000 and then worked on 20000/60000 . BUt why did we round off 21120 to 20,000 and why 64,000 to 60,000.

Is there a rule to round these number off.

Please see if anyone can help here. If anyone has PR manual then this problem appears on page# 65.

thanks
Jawad Shah
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Source: — Problem Solving |

by pepeprepa » Sun Jul 20, 2008 3:01 am
I think what is important is to round off to something simple first.

In your example 1120 from 21120 and 4000 from 64000 is good because you now have simple numbers.

The second good thing is that what is removed in the numerator and the denominator does not change a lot the ratio, both things are in the same proportion, 1120/21120 and 4000/64000 are more or less the same.
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