Question:
Find the sum of the GP :
$0.15+0.015+0.0015+\ldots .$ To 6 terms
Solution:
Sum of a G.P. series is represented by the formula, $\mathrm{S}_{\mathrm{n}}=\mathrm{a} \frac{1-\mathrm{r}^{\mathrm{n}}}{1-\mathrm{r}}$
when |r|<1. ‘Sn’ represents the sum of the G.P. series upto nth terms, ‘a’ represents the first term, ‘r’ represents the common ratio and ‘n’ represents the number of terms
Here,
a = 0.15
r = (ratio between the n term and n-1 term) 0.015 ÷ 0.15 = 0.1
n = 6 terms
$\Rightarrow \mathrm{S}_{\mathrm{n}}=0.15 \times \frac{1-0.1^{6}}{1-0.1}$
$\Rightarrow \mathrm{S}_{\mathrm{n}}=0.15 \times \frac{1-0.000001}{0.9}$
$\Rightarrow \mathrm{S}_{\mathrm{n}}=0.15 \times \frac{0.999999}{0.9}$
$\therefore \mathrm{S}_{\mathrm{n}}=16.67$