Answer:
S20 ≈ 4.942
Explanation:
Sum of a geometric series is expressed as Sn = a(1-rⁿ)/1-r if r<1
a is the first term
r is the common ratio
n is the number of terms
Given the geometric series
1 + 0.8 + 0.8^2 +0.8^3 + ... + 0.8^{19}
Given a = 1,
r = 0.8/1 = 0.8²/0.8 = 0.8
n = 20 (The total number of terms in the series is 20)
Substituting this values in the formula above.
S20 = 1(1-0.8^20)/1-0.8
S20 = 1-0.01153/0.2
S20 = 0.9885/0.2
S20 ≈ 4.942