1. **State the problem:** Calculate the sum of 1.5 and 0.8. 2. **Formula used:** Addition of decimal numbers is straightforward: $$a + b = c$$ where $a=1.5$ and $b=0.8$. 3. **Perform the addition:** $$1.5 + 0.8 = 2.3$$ 4. **Explanation:** When adding decimals, align the decimal points and add the numbers as usual. Here, 1.5 plus 0.8 equals 2.3. **Final answer:** $$2.3$$