V = Bh, where B is the area of the base of the pyramid and h is the height. Therefore, the
volume of the pyramid is (15)(4) = 20. However, you need to subtract the volume of the
semispherical indentation in the base. Once again, the reference sheet found beginning of the
Math section tells you that the volume of a sphere is given by the equation V = πr^3 . Because
the diameter of the indentation is 2 cm, the radius of the hemisphere is 1 cm. If it were a whole
sphere, the volume of the indentation would be π(1)^3 = 4.189; you want only half, so dividing
by 2 gives you 2.094 cm^3 for the hemisphere. Subtracting 2.094 cm^3 from the 20 cm^3 of the
pyramid gives you a total volume of 20 – 2.094 = 17.906 cm^3 . Finally, you can find the density
of Lucite by using the definition of density: Density = ≈ 1.18 g/cm^3 , which is (B).