Which equation could be used to calculate the sum of the geometric series? 1/4+2/9+4/27+8/81+16/243?

From the given sequence:

1/4, 2/9, 4,27, 8/81, 16/243

the common ratio is: 2/3

thus the sum of the series will be given by the formula:

Sn=[a (1-r^n) ] / (1-r)

plugging the values we obtain:

Sn=[1/4 (1 - (2/3) ^n) ] / (1-2/3)

thus the equation that will be used to find the sum is:

Sn=3[1/4-1/4 (2/3) ^n]

=3/4[1 - (2/3) ^n]