How many terms of the series 2 + 6 + 18 + …. + must be taken to make the sum equal to 728?

Question

Philoid · Accepted Answer

Sum of a G.P. series is represented by the formula, , when r>1. ‘S_n’ represents the sum of the G.P. series upto n^th terms, ‘a’ represents the first term, ‘r’ represents the common ratio and ‘n’ represents the number of terms.

Here,

a = 2

r = (ratio between the n term and n-1 term) 6 ÷ 2 = 3

S_n = 728

∴

⇒

∴

∴ 6 terms must be taken to reach the desired answer.