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# (99999)^2-1^2

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Senior Manager
Status: Math is psycho-logical
Joined: 07 Apr 2014
Posts: 432
Location: Netherlands
GMAT Date: 02-11-2015
WE: Psychology and Counseling (Other)

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28 Feb 2015, 05:05
chetan2u wrote:
pacifist85 wrote:
I did it sort of differently, but looks simpler to me...:

99999^2 - 1 = (3^2 * 11111) - 1 = 99999 - 1 = 99998

From the answer choices we eliminate A and B right away, and move to C which is:
10^5 - 2 = 100000 - 2 = 99998.

Right...??

hi pacifist,
you have missed out the power 2 of 99999..
and C is 10^5(10^5-2)

Yes, I was just realizing exactly that! Also, I very conveniently decided to ignore the first part of answer C. Which worked like charm! Hahahahaha!

Thank you though!
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Joined: 09 Sep 2013
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22 Feb 2017, 13:23
Hello from the GMAT Club BumpBot!

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Joined: 19 Apr 2016
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GMAT 1: 570 Q48 V22
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22 Feb 2017, 22:34
TheRob wrote:
$$99999^2-1^2$$ =

A) $$10^5$$
B) $$10^{10}$$
C) $$(10^5)(10^5-2)$$
D) $$(10^5)(10-2)$$
E) $$(10^{10})(10^{10}-2)$$

$$(a^2-b^2) =(a+b)(a-b)$$

$$99999^2-1^2$$

= (99999-1)(99999+1)

= (100000-2)(100000)

$$= (10^5-2)(10^5)$$

Hence Option C is correct
Hit Kudos if you liked it
(99999)^2-1^2   [#permalink] 22 Feb 2017, 22:34

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