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Bunuel
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K-9 must be divisible by 9

2^n - 2

B is the answer

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Bunuel
\(k = 2^n + 7\), where n is an integer greater than 1. If k is divisible by 9, which of the following MUST be divisible by 9?


A. \(2^n - 8\)

B. \(2^n - 2\)

C. \(2^n\)

D. \(2^n + 4\)

E. \(2^n + 5\)

A quick Approach:



\(k = 2^n + 7\) and k is divisible by 9

An easy value of n for which k is divisible by 9 is n=1

@n = 1, \(k = 2^1 + 7 = 9\) i.e. Divisible by 9

Now, let's check options

A. \(2^n - 8 = 2^1-8 = -6\) NO

B. \(2^n - 2 = 2^1 - 2 = 0\) YES

C. \(2^n = 2^1 = 2\) NO

D. \(2^n + 4 = 2^1 + 4 = 6\) NO

E. \(2^n + 5 = 2^1 + 5 = 7\) NO

ANswer: Option B

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Dear,
If it’s given that n > 1 then?
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I think my approach would be on deducing the value of n, which comes out to be 7.

k=2^7 + 7 = 135 (Divisible by 9)

Now use this value to check the answers. 2^n-2 will be divisible by 9
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