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What is the highest prime factor in the expression

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shadowcatradz
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What is the highest prime factor in the expression [#permalink] New post   Updated on: 12 Dec 2017, 11:55
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What is the highest prime factor in the expression

\(\frac{3^{18} - 3^{12}}{3^5}\)

A) 3

B) 7

C) 11

D) 13

E) 19
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Official Answer
D

Originally posted by shadowcatradz on 20 Feb 2017, 09:57.
Last edited by Carcass on 12 Dec 2017, 11:55, edited 3 times in total.
Edited by Carcass
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sandy
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Re: What is the highest prime factor in the expression [#permalink] New post   20 Feb 2017, 12:31
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Explanation

Take the expression

\(\frac{3^1^8 - 3^1^2}{3^5}\) or \(3^1^2\frac{3^6 - 1}{3^5}\)= \(3^7 \times 728\).

Clearly the highest prime factor of the expression \(\frac{3^1^8 - 3^1^2}{3^5}\) also is the highest prime factor of 728.

Try \(\frac{728}{19}\). Doesn't work!

Try \(\frac{728}{13}\). Works!

Hence D is the right answer.
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gmatclubot
Re: What is the highest prime factor in the expression [#permalink]
20 Feb 2017, 12:31
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