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# Exponents

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Manager
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Exponents [#permalink]  28 Aug 2009, 05:50
00:00

Difficulty:

(N/A)

Question Stats:

50% (02:47) correct 50% (00:00) wrong based on 2 sessions
99999^2-1^2
Manager
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Re: Exponents [#permalink]  28 Aug 2009, 05:52

A) 10^5
B) 10^10
C) (10^5)(10^2-2)
D) (10^5)(10-2)
E) (10^10)(10^10-2)
Manager
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Re: Exponents [#permalink]  28 Aug 2009, 05:56
I did it in my head, so C? anyone else
Senior Manager
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Re: Exponents [#permalink]  28 Aug 2009, 06:14
I am trying to do it, but can not find the answer I got among answers:

9999^2-1^2

(9999+1)(9999-1)
Thus getting 10 0000 (9998).
We can rearrange that as 10^5(10^-2). But there is no such answer in there though
_________________

Never give up,,,

Manager
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Re: Exponents [#permalink]  28 Aug 2009, 06:55
it is C!!!!! thanks your explanation I got to the right path

her it comes

99999^2-1^2

(100000–1)^2–(1^2)=

(10^5)^2 – 2(10^5)+1–1=

(10^5)(10^2–2)
Intern
Joined: 30 Jun 2009
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Re: Exponents [#permalink]  28 Aug 2009, 07:30
TheRob wrote:
it is C!!!!! thanks your explanation I got to the right path

her it comes

99999^2-1^2

(100000–1)^2–(1^2)=

(10^5)^2 – 2(10^5)+1–1=

(10^5)(10^2–2)

Can you pls elaborate how you moved from
(10^5)^2 – 2(10^5)+1–1
to
(10^5)(10^2–2)
Manager
Joined: 10 Aug 2009
Posts: 130
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Re: Exponents [#permalink]  28 Aug 2009, 07:59
defoue wrote:
TheRob wrote:
it is C!!!!! thanks your explanation I got to the right path

her it comes

99999^2-1^2

(100000–1)^2–(1^2)=

(10^5)^2 – 2(10^5)+1–1=

(10^5)(10^2–2)

Can you pls elaborate how you moved from
(10^5)^2 – 2(10^5)+1–1
to
(10^5)(10^2–2)

It should be (10^5)^2-2\times 10^5=10^5\times (10^5-2)...I believe it is a mistake...
Manager
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Re: Exponents [#permalink]  28 Aug 2009, 08:08
This question can be solved the same way as what is 99^2?

Personally I can't do 99x99 in my head. But I can easily do (99x100) - 99 which would give the same result.

Here we do the same thing 99,999x 100,000 - 99,999

= 9,999,900,000 - 99,999 = 9,999,800,001 - now subtract 1^2

All that remains is to figure out the exponents. 10^5 takes care of the 0's and 10^5-2 should take care of the remainder. Unfortunately that doesn't look like any answer given. Are you sure answer choices are correct?

Manager
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Re: Exponents [#permalink]  28 Aug 2009, 09:31
Can you pls elaborate how you moved from
(10^5)^2 – 2(10^5)+1–1
to
(10^5)(10^2–2)

well I factorized 10^5 from the terms

(10^5)(10^2 -2 ) + 1 - 1
Manager
Joined: 10 Jul 2009
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Re: Exponents [#permalink]  28 Aug 2009, 10:11
Manager
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Re: Exponents [#permalink]  28 Aug 2009, 10:27
TheRob wrote:
Can you pls elaborate how you moved from
(10^5)^2 – 2(10^5)+1–1
to
(10^5)(10^2–2)

well I factorized 10^5 from the terms

(10^5)(10^2 -2 ) + 1 - 1

Your factorization is not correct, please see my previous post regarding it.
Manager
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Re: Exponents [#permalink]  28 Aug 2009, 12:24
Answer should be 10^5(10^5 - 2)..

10^5 * 10^2 = 10^7 (not 10^10)

10^5 * 10^5 = 10^10
Manager
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Re: Exponents [#permalink]  29 Aug 2009, 00:08
TheRob wrote:
99999^2-1^2

99999^2-1^2
=(99999+1)(99999-1)
=100000*99998
=9999800000
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Kudos me if my reply helps!

Manager
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Re: Exponents [#permalink]  31 Aug 2009, 05:23
It is true my factorization is wrong

99999^2-1^2

(99999-1)(99999+1)

(100000-2)(100000)

(10^5 - 2) (10^5)

What do you think?
Re: Exponents   [#permalink] 31 Aug 2009, 05:23
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