Question

Find the sum of $16.2,5.4,1.8,....$ upto $7$ terms.

Answer 1

Clearly the given series is G.P with common ratio $r=\frac{1}{3}$ and first term $a=16.2$
$S_n$ be sum first n terms of G.P
Formula for sum of $n$ terms of G.P. is given by
$S_n=\frac{a(r^n-1)}{r-1}$

$S_7=\frac{16.2\times ({\left(\frac{1}{3}\right)}^7-1)}{\frac{1}{3}-1}=\frac{1093}{45}$.