1) If $2^{n-1}+2^{n+1}=320$ then n is equal to: A) 6 B) 8 C) 5 D) 7 Answer: Option DExplanation:$2^{n-1}+2^{n+1}=320$ $\Leftrightarrow 2^{n-1} \left( 1+ 2^{2}\right)=320$ $\Leftrightarrow 5 \times 2^{n-1} = 320$ $\Leftrightarrow 2^{n-1} = \frac{320}{5}$ $=64=2^{6}$ $\Leftrightarrow n-1=6$ $\Leftrightarrow n=7$
