The sum of first 20 terms of the sequence 0.7, 0.77, 0.777, .. , is (1) `7/9(99-10^(-20))` (2) `7/(81)(179+10^(-20))` (3) `7/9(99+10^(-20))` (3) `7/(81)(179-10^(-20))`

Explanation

To find the sum of the first 20 terms of the sequence 0.7, 0.77, 0.777, ..., we can observe that the terms can be expressed in a more manageable form.

### Step-by-Step Solution:

1. **Identify the Pattern**:
The sequence can be expressed as:
- 1st term: 0.7 = 0.7
- 2nd term: 0.77 = 0.7 + 0.07
...