FIND

series can be written as (1-1/3) +(1-1/9) + (1-1/27) +....................................n terms

taking all 1 one side we get for n terms    n - (1/3 +1/9 +1/27 +1/81...............n terms )  which is a GP with first term 1/3 and r =1/3

so sum is  n - (1/3){1-(1/3)ⁿ}/ 1-1/3

which gives B as correct answer