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by sam2304 » Mon May 21, 2012 7:21 pm
99,999^2 - 1^2. This is of form a^2 - b^2

= [a+b]*[a-b]
= [99,999+1]*[99999-1]
= [100,000]*[100000-2]
= 10^5[10^5-2]

IMO E
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by Anurag@Gurome » Mon May 21, 2012 7:23 pm
alex.gellatly wrote:99,999^2 - 1^2 =

A. 10^10 - 2
B. (10^5 - 2)^2
C. 10^4(10^5 - 2)
D 10^5(10^4 - 2)
E. 10^5(10^5 - 2)
Apply the formula, a² - b² = (a + b)(a - b)
So, 99,999^2 - 1^2 = (99999 + 1)(99999 - 1)
= 100000(10^5 - 2)
= [spoiler](10^5)(10^5 - 2)[/spoiler]

The correct answer is E.
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