Paper thickness varies. Typically, 100 sheets are about a cm thick. Atoms typically vary from 1 to 3 -10 angstroms in radius. (An angstrom is 10 m.) Suppose a piece of paper is 0.0084cm thick. How many atoms span the thickness if the radius of the atom is 3.08 angstroms? In a problem like this a lot of irrelevant (to problem solving) information is given. It helps to write out what useful information is given and what you are going to solve for.