posted a question
Use differentials to estimate the amount of material in a closed cylindrical can that is 70 cm high and 28 cm in diameter if the metal in the top and bottom is 0.1 cm thick, and the metal in the sides is 0.05 cm thick.

Remember we are estimating the amount of material here, not trying to find an exact representation of the amount of material used. How can a differential of the volume of a cylinder help with this?