Correct Answer - Option 2 : 1999

**Calculations:**

According to the question, we have

Greatest 3 digit number = 999

Smallest 4 digit number = 1000

Now, The sum of the greatest 3 digit number and the smallest 4 digit number

⇒ Sum = 1000 + 999

⇒ Sum = 1999

**∴ The sum of the greatest 3 digit number and the smallest 4 digit number is 1999.**