Question

Find the sum of the first 5 terms of the GP : 1 + 2/3 + 4/9 + ......=

• A. 215/81
• B. 211/81
• C. 209/81
• D. 225/81

Answer 1

Answer:

B. 211/81

$a=1, r= (2/3)/1=2/3$

$S_n=\frac{a(1-r^n)}{(1-r)}$

$S_5=\frac{1(1-(2/3)^5)}{1-2/3}$

$=\frac{1-(32/243)}{1/3}$

$=3(\frac{243-32}{243})$

$=211/81$