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2 of 2 that got away

by SoftwareDrone » Sun Aug 05, 2012 5:30 pm
After completing the GMAT Prep Now video sessions, I am happy to report that I scored a 640 on my practice test today. This is great, considering my first (and only so far) attempt at the GMAT (before the GMAT Prep Now videos) yielded a 430. There were two math problems in particular that didn't seem so difficult at first glance, yet I cannot seem to push through. The second one is:

10^8 - 10^2 / 10^7 - 10^3.

I thought to do this: 10^2(10^6 - 1) / 10^3(10^4 - 1), but cannot figure out how to go further.
Please help me O Gurus.
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by GMATGuruNY » Sun Aug 05, 2012 7:22 pm
The value of (10^8-10^2)/(10^7-10^3) is closest to which of the following?

a)1
b)10
C)10^2
d)10^3
e)10^4
Please always post the answer choices.

Since this question asks for an APPROXIMATION, 10² and 10³ can safely be ignored here: these values are VERY, VERY SMALL relative to 10� and 10�.
Thus:
(10� - 10²) / (10� - 10³) ≈ 10�/10� = 10.

The correct answer is B.
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by SoftwareDrone » Sun Aug 05, 2012 8:19 pm
Sorry about that. I would have written down the answer choices had I had them. I only had the problem from scribbling it down during the test.
Good point about the relative size of the numbers.
Thanks!
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