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# If 5^21 x 4^11 = 2 x 10^n, what is n? a. 11 b. 21 c. 22 d.

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If 5^21 x 4^11 = 2 x 10^n, what is n? a. 11 b. 21 c. 22 d. [#permalink]  12 Jan 2008, 13:27
If 5^21 x 4^11 = 2 x 10^n, what is n?

a. 11
b. 21
c. 22
d. 23
e. 32
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Re: number property problem [#permalink]  12 Jan 2008, 14:22
5^21 x 2^22 = 2x5^n x 2^n
5^21 x 2^22 = 5^n x 2^(n+1)
n=21
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Re: number property problem [#permalink]  12 Jan 2008, 15:01
5^21x4^11=2x10^n

Divide both sides by 2

(5^21x4^11)/2 =10^n

Simplify 4^11 to 2^22

(5^21x2^22)2^1=10^n
5^21X2^21=10^n
10^21=10^n
n=21
Re: number property problem   [#permalink] 12 Jan 2008, 15:01
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