1. The problem is to calculate the division of 20 by 5. 2. The formula for division is $\frac{a}{b}$ where $a$ is the numerator and $b$ is the denominator. 3. Substitute the values: $\frac{20}{5}$. 4. Simplify the fraction by dividing numerator and denominator by their greatest common divisor, which is 5. 5. Show the cancellation: $$\frac{\cancel{20}}{\cancel{5}} = \frac{4}{1}$$. 6. The result is $4$ because dividing by 1 leaves the number unchanged. 7. Therefore, $20 \div 5 = 4$.