How many terms are there in the GP 5, 20, 80, 320……….. 20480?
A. 5 B. 6 C. 8 D. 7 Answer: Option DShow Answer
Solution(By Apex Team)
Common ratio, r = $\Large\frac{20}{5}$ = 4
Last term or nth term of GP = $a r^{n-1}$
$\begin{aligned}&20480=5\times\left(4^{n-1}\right)\\
&\text{ Or, }4^{n-1}=\frac{20480}{5}=4^8\end{aligned}$
So, comparing the power,
Thus, n – 1 = 8
Or, n = 7
Number of terms = 7
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