Percent: part, whole and percent

Sometimes we know a part and its percent and need the whole. Draw a tape for 100% and cut it into equal parts that fit the percent. If 20% is 12, then 20% is one fifth of the tape, so the five equal parts are 12 each and the whole is 5 × 12 = 60. If 15% is 45, cut the tape into pieces of 5%: 15% is three pieces, so one piece is 45 ÷ 3 = 15; 100% has 20 pieces, so the whole is 20 × 15 = 300. A 10 × 10 grid does the same job: each small square is 1% of the whole. Always check by taking the percent of your answer.