To start this lower-elementary-level activity, start by asking for two volunteers. One will sit behind a table with three toys labeled with price tags from one to three dollars. Give the other student five one dollar bills, telling the class how many dollars you gave him. Ask the latter student to "buy" a toy from the former with the money. Afterward, ask the student to count the bills he has left, explaining that this is subtraction. Tell the student to "buy" another toy, then ask the seller to add the two totals together to find how many bills he has now, explaining that this is addition.
For students who are just learning to identify geometric shapes, a dollar bill provides numerous examples. Give students either pictures of both sides of a dollar bill or, for more mature or responsible classes, actual dollar bills, and have them identify as many different shapes as they can on a separate piece of paper. Afterward, put an example of a dollar on the overhead board and ask for volunteers to label the shapes they found. Ask students to identify the main features of the shape — for example, the face of the pyramid beneath the Eye of Providence is a triangle because it has three sides.
The day before doing this activity, ask students to bring in a dollar bill to the next day's class. Give students rulers and have them measure 10 different shapes on either side of their dollars and find their areas. The main goal of this activity is for students to review area equations, so require them to look up the equations on their own using their books or notes.
Every dollar bill has unique features, such as a its serial number and year of printing. Show students an example of both sides of a dollar, and have them come up with as many questions as they can about the probability of any given bill having a certain feature — for example, "The probability of an even serial number," which would be 1:2. Have students share their questions and answer them as a class. Students should research the answers for the questions that can't be answered off-hand and present their findings in the next class.