Bunuel
If n is a positive integer, is \(3^4+3^{n+4}\) divisible by 5?
(1) n is an even integer.
(2) \(3^8 +3^{n+8}\) is divisible by 5.
Question:
\(3^4+3^{n+4}\)
\(3^4(1+3^{n})\)
\(3^4\) is not divisible by 5. Hence for the entire expression \(3^4(1+3^{n})\) to be divisible by 5, the term \((1+3^{n})\) should be divisible by 5.
Target Question: Is \(1+3^{n}\) divisible by 5 ?
Statement 1 (1) n is an even integer.If n = 2; \(1+3^{n}\) = 10
Is \(1+3^{n}\) divisible by 5 ? - Yes !
If n = 4; \(1+3^{n}\) = 82
Is \(1+3^{n}\) divisible by 5 ? - No !
As we have multiple answers for the same target question, the statement alone is not sufficient.
Statement 2 (2) \(3^8 +3^{n+8}\) is divisible by 5.\(3^8 +3^{n+8}\) is divisible by 5.
\(3^8(1 + 3^{n})\) is divisible by 5
\(3^8\) is divisible not by 5, therefore \((1 + 3^{n})\) must be divisible by 5 for the entire term to be divisible by 5.
Is \(1+3^{n}\) divisible by 5 ? - Yes !
The statement alone is sufficient to answer.
Option B