1. **State the problem:** We need to find the sum of the numbers 9.09, 2.77, and 5.49. 2. **Formula used:** To add numbers, we use the addition operation: $$a + b + c$$ where $a=9.09$, $b=2.77$, and $c=5.49$. 3. **Perform the addition step-by-step:** $$9.09 + 2.77 = 11.86$$ 4. **Add the last number:** $$11.86 + 5.49 = 17.35$$ 5. **Final answer:** $$\boxed{17.35}$$ The sum of 9.09, 2.77, and 5.49 is 17.35.