Lesson objective: Practice using a double number line to determine a number when a percent of it is known.

Related to finding a percent of a number, a double number can also be used to find a number when a percent of it is known. A double number line is used here because this model supports use of benchmark percents to determine the value related to 100%. This work develops students' understanding that percent is a special ratio comparing one number with 100.

Students engage in Mathematical Practice #2: Students** **reason abstractly and quantitatively as they focus on the part, the whole and the percent in a given situation.

**Key vocabulary:**

- benchmark percent

**Special materials needed:**

- graph paper