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

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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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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.

Spoiler: OA

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

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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 $9^9 - 9^2=9^2(9^7-1)=9^2*9^7=9^9
ans C..$
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Math Revolution GMAT Instructor

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

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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.
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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

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.

Answer: C
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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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