Find the sum of the indicated terms of the geometric sequence. 5, 20, 80 ... (to 5 terms)
A)s = 1,705
B)s = 1,700
C)s = 1,710
D)s = 1,715
E)none of the above

Question

Quizplus · Accepted Answer

The sequence is geometric with the first term a = 5 and common ratio r = 4. The sum of the first 5 terms is given by the formula S_n = a(1-r^n)/(1-r). Substituting the values, S_5 = 5(1-4^5)/(1-4) = 5(1-1024)/(-3) = 5(-1023)/(-3) = 5*341 = 1705.

Find the Sum of the Indicated Terms of the Geometric