Given: 0.15, 0.015, 0.0015,... 20 terms.

Sum of n terms of a G.P. is given by: (a: First term of G.P, r: common difference of G.P, n: Number of terms of the G.P)

First term of the Given G.P (a) = 0.15

Common difference of the given G.P(r) = = = 0.1

Number of terms(n): 5

Let the sum of 20 terms be s

∴ The sum of 20 terms of the given sequence is: [1-(0.1)²⁰]