The sum of first 20 terms of the sequence
Question:

The sum of first 20 terms of the sequence 0.7, 0.77, 0.777, ……, is :

1. $\frac{7}{81}\left(179-10^{-20}\right)$

2. $\frac{7}{9}\left(99-10^{-20}\right)$

3. $\frac{7}{81}\left(179+10^{-20}\right)$

4. $\frac{7}{9}\left(99-10^{-20}\right)$

Correct Option: , 3

Solution: