Evaluate 12 sigma n=3 20 (0.5) ^n-1

9.99

19.95

29.98

39.96

Answer: Is D

We have a geometric series in which:

a = 20

r = 1/2

Now, we know that: S2 = 20 (1-r^2) / (1-r) and S12 = 20 (1-r^12) / 1-r

Therefore: sigma (3,12) = S12-S2 = 20[ (1-r^12) / (1-r) - (1-r^2) / (1-r) ] = 5115/512 = 9.99023438

Therefore, the answer is: 9.99