How many terms of G.P. `3,3^2,3^3,dotdotdot`are needed to give the sum 120?

Answer

N/a

Explanation

Let the sum of n terms be 120.
Here `a=3`
`r=3`
`S_(n)=120`
`implies(3(3^(n)-1))/(3-1)=120implies3^(n)-1=80`
`implies 3^(n)=81=3^(4)impliesn=4`