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# 9^9 - 9^2 is approximation of which of the following?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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9^9 - 9^2 is approximation of which of the following?  [#permalink]

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03 Mar 2016, 18:25
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15% (low)

Question Stats:

75% (00:48) correct 25% (00:45) wrong based on 83 sessions

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9^9 - 9^2 is approximation of which of the following?

A. 9^7
B. 9^8
C. 9^9
D. 9^11
E. 9^10

* A solution will be posted in two days.

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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"Only $79 for 1 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Math Expert Joined: 02 Aug 2009 Posts: 7945 Re: 9^9 - 9^2 is approximation of which of the following? [#permalink] ### Show Tags 03 Mar 2016, 20:00 MathRevolution wrote: 9^9 - 9^2 is approximation of which of the following? A. 9^7 B. 9^8 C. 9^9 D. 9^11 E. 9^10 * A solution will be posted in two days. It can be straight way seen from the equation that 9^9 is much higher than 9^2 and addition or subtraction of 9^2 from 9^9 will not make much difference.. so $$9^9 - 9^2$$ should be nearly equal to C$$9^9$$.. Other way would be factorization.. $$9^9 - 9^2=9^2(9^7-1)..$$ .. 1 is way too small quantity in comparison to 9^7.. so (9^7-1)=9^7.. so $$9^9 - 9^2=9^2(9^7-1)=9^2*9^7=9^9 ans C..$$ _________________ Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7999 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: 9^9 - 9^2 is approximation of which of the following? [#permalink] ### Show Tags 06 Mar 2016, 03:51 9^9 - 9^2 is approximation of which of the following? A. 9^7 B. 9^8 C. 9^9 D. 9^11 E. 9^10 => Since 9^2 is a small number compared to 9^9, it can be disregarded. Thus, 9^9-9^2=9^9 is derived and the answer is C. _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$79 for 1 month Online Course"
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Re: 9^9 - 9^2 is approximation of which of the following?  [#permalink]

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02 May 2017, 16:52
1
MathRevolution wrote:
9^9 - 9^2 is approximation of which of the following?

A. 9^7
B. 9^8
C. 9^9
D. 9^11
E. 9^10

We can simplify the given expression:

9^9 - 9^2

9^2(9^7 - 1)

Since 9^7 - 1 is almost the same as 9^7, we have:

9^2 x 9^7 = 9^9.

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Re: 9^9 - 9^2 is approximation of which of the following?  [#permalink]

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05 Feb 2019, 01:13
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Re: 9^9 - 9^2 is approximation of which of the following?   [#permalink] 05 Feb 2019, 01:13
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