SPM Practice 2 (Geometric Progression) : Question 9

Question 9

In a geometric progression, the first term is 18 and the common ratio is r.
Given that the sum to infinity of this progression is 21.6, find the value of r.

[ Remember the formula for sum to infinity ${S}_{\infty }=\frac{a}{1-r},\text{​}\text{​}\text{\hspace{0.17em}}\text{\hspace{0.17em}}-1 ]