Question 1191585
<br>
The 4th term 81 is the 3nd term 9, multiplied by the common ratio twice:<br>
{{{81=9r^2}}}
{{{9=r^2}}}
{{{r=3}}} or {{{r=-3}}}<br>
There are two possible answers to the problem.<br>
(1) r=3; the first four terms are 3, 9, 27, 81; sum 120
(2) r=-3; the first four terms are -3,9,-27, 81; sum 60<br>