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I must have been missing something here. Appreciate your

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Manager
Joined: 21 Sep 2006
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I must have been missing something here. Appreciate your [#permalink]  21 Sep 2007, 19:58
I must have been missing something here. Appreciate your help.

(5^21)(4^11)=2(10^n). What is the value of n?

A. 11
B. 21
C. 22
D. 23
E. 32
Director
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Re: GMAT Prep: Exponents [#permalink]  21 Sep 2007, 20:03
Hang Tuah wrote:
I must have been missing something here. Appreciate your help.

(5^21)(4^11)=2(10^n). What is the value of n?

A. 11
B. 21
C. 22
D. 23
E. 32

you have to change the bases so both sides will be comparable:
(5^21) (2^2)^11 = 2 * 2^n * 5^n
(5^21) (2^22) = 2 * 2^n * 5^n
divide both sides by 2 and you will be left with
(5^21) (2^21) = 2^n * 5^n
n = 21
Manager
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Re: GMAT Prep: Exponents [#permalink]  21 Sep 2007, 22:12
Hang Tuah wrote:
I must have been missing something here. Appreciate your help.

(5^21)(4^11)=2(10^n). What is the value of n?

A. 11
B. 21
C. 22
D. 23
E. 32

Gotta get good at exponents...grr Expect to see at least one of these on the GMAT. Ok here goes...

(5^21)(2^2)^11=2(5^n*2^n)

5^21*2^22=2(5^n*2^n) ---> divide the 2. 5^21*2^21=5^n*2^n

U can multiply the numbers now b/c they have the same exponents.

10^21=10^n ---> n = 21. Note you don't have to split up the 10^n to 5^n*2^n. But in my case, doings o helped me solve the problem.

Ans B.
Re: GMAT Prep: Exponents   [#permalink] 21 Sep 2007, 22:12
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