1. The problem is to understand the number 10.5. 2. 10.5 is a decimal number, which means it has a whole number part and a fractional part separated by a decimal point. 3. The whole number part is 10, and the fractional part is 0.5. 4. The fractional part 0.5 can be expressed as the fraction $\frac{1}{2}$. 5. Therefore, 10.5 can be written as $10 \frac{1}{2}$ or $\frac{21}{2}$ in improper fraction form. 6. This number is a rational number because it can be expressed as a ratio of two integers. Final answer: 10.5 or $10 \frac{1}{2}$ or $\frac{21}{2}$.