A soil sample has a bulk density of $1.5 \ \text{g/cm}^3$ and a particle density of $2.5 \ \text{g/cm}^3$. What is the percentage porosity of the soil?

Porosity is calculated as $\left(1 - \dfrac{\text{Bulk Density}}{\text{Particle Density}}\right) \times 100$. Substituting the values: $\left(1 - \dfrac{1.5}{2.5}\right) \times 100 = (1 - 0.6) \times 100 = 40\%$. Common errors include subtracting particle density from bulk density directly (giving a negative value) or dividing incorrectly to obtain 30% or 60%.