ABC26GN1951 · Surds and Indices

Subject: General Aptitude · Chapter: Surds and Indices · Exam: · Marks: · Difficulty:

If $2^{n-1}+2^{n+1}=320$, then $n$ is equal to
(a)6
(b)8
(c)5
(d)7
Answer
Answer (as printed): D
Explanation
$2^{n-1}+2^{n+1}=320 \Leftrightarrow 2^{n-1}\left(1+2^{2}\right)=320 \Leftrightarrow 5 \times 2^{n-1}=320 \Leftrightarrow 2^{n-1}=\frac{320}{5}=64=2^{6} \Leftrightarrow n-1=6 \Leftrightarrow n=7.$

Explanation as extracted from the printed page; notation may be imperfect.

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