1. The problem is to divide 4 by 5. 2. The division formula is $\frac{a}{b}$ where $a$ is the numerator and $b$ is the denominator. 3. Here, $a=4$ and $b=5$, so the division is $\frac{4}{5}$. 4. This fraction cannot be simplified further because 4 and 5 have no common factors other than 1. 5. Therefore, the final answer is $\frac{4}{5}$ or 0.8 in decimal form.