GMatAspirerCA wrote:

Hi

I am totally going wrong in doing simple math multiplication and division while dealing with large numbers. Either they are taking way too longer and ending up in a mistake.

For example question here,

a-circular-mat-with-diameter-20-inches-is-placed-on-a-square-55871.html100 pi / 24*24

I came till here but some where making a mistake in coming to approximate proportion this fraction is close to. Any suggestions in this regard are much appreciated.

Dear

GMatAspirerCA,

I'm happy to help.

First of all, here are a couple blogs you may find germane:

http://magoosh.com/gmat/2012/fractions-on-the-gmat/http://magoosh.com/gmat/2012/the-power- ... mat-quant/First of all, you are correct that the proportion is \(\frac{100pi}{24*24}\)

We can cancel one factor of 4 in the numerator and denominator, which leaves us with: \(\frac{25pi}{6*24}\)

Now, here's what I notice: 25/24 is exceptionally close to one, and pi is about 3, which means that (pi)/6 is close to 1/2. So we have something close to 1 times something close to 1/2, which would have to be close to 1/2. Answer =

(C).

Whenever you have to approximate with pi, for most purposes 3 is a close enough approximation. If we are being really detailed about it, in some of the harder questions we might have to use 22/7, which is even more accurate.

Does this answer all your questions?

Mike

_________________

Mike McGarry

Magoosh Test Prep

Education is not the filling of a pail, but the lighting of a fire. — William Butler Yeats (1865 – 1939)