Given data:
The given common ratio is r=1/3.
(a)
The expression for the common ratio of first series is,
r=27/81
=1/3
(b)
The expression for the common ratio of second series is,
r=3/1
=3
(c)
The expression for the common ratio of second series is,
r=12/9
=4/3
(d)
The expression for the common ratio of second series is,
r=-3/1
=-3
Thus, the first option has 1/3 common ratio.
