A cuboid with dimensions 4 cm, 2 cm, and 2.5 cm has a density of 2000 kg/m³. Calculate its mass in grams.

The dimensions of the cuboid are 4 cm, 2 cm, and 2.5 cm.

$$V = \text{length} \times \text{width} \times \text{height}$$ $$V = 4\, \text{cm} \times 2\, \text{cm} \times 2.5\, \text{cm}$$ $$V = 20\, \text{cm}^3$$

We know that $1\, \text{m} = 100\, \text{cm}$, so $1\, \text{m}^3 = (100\, \text{cm})^3 = 1,000,000\, \text{cm}^3$.

$$V = 20\, \text{cm}^3 \times \frac{1\, \text{m}^3}{1,000,000\, \text{cm}^3}$$ $$V = 0.00002\, \text{m}^3$$

The density ($\rho$) is 2000 kg/m³. The formula for density is $\rho = \frac{m}{V}$, where $m$ is mass and $V$ is volume.
Rearranging for mass, we get $m = \rho \times V$.

$$m = 2000\, \frac{\text{kg}}{\text{m}^3} \times 0.00002\, \text{m}^3$$ $$m = 0.04\, \text{kg}$$

We know that $1\, \text{kg} = 1000\, \text{g}$.

$$m = 0.04\, \text{kg} \times \frac{1000\, \text{g}}{1\, \text{kg}}$$ $$m = 40\, \text{g}$$

The mass of the cuboid is $\text{40 g}$.