2.If the density of gold is 20 g/mL , what is the mass of a 40 cm^3 bar.

Here's how to solve this problem:<br /><br />1. **Unit Conversion:** Notice that the density is given in g/mL, while the volume is in cm³. Since 1 mL = 1 cm³, we can use the given volume directly.<br /><br />2. **Formula:** Density is defined as mass divided by volume: Density = Mass/Volume<br /><br />3. **Solve for Mass:** We can rearrange the formula to solve for mass: Mass = Density * Volume<br /><br />4. **Calculation:** Mass = (20 g/mL) * (40 cm³) = 800 g<br /><br />Therefore, the mass of the gold bar is $\boxed{800}$ g.<br />