The part is 8 and the whole is 40. You need to find the percent.

Let n represent the percent.

Part = percentwhole

8 = n40                       (Substitute part = 8 and whole = 40)

               (Divide each side by 40)

                        (Cancel common terms)

                         (Divide: )

           (Multiply with 100 and add percent sign)

                        (Multiply: )

8 is 20 of 40.