# Mr. R.’s World of Math

## pen exemplar: making change of a dollar

Lesson: The Pen Problem
Lesson Aim: use grid paper to graphically represent how to make change of a dollar.
Materials: Grid Paper and Images of pens (or any other items with prices less than a dollar)

For your birthday, your uncle has sent you a \$1 gift certificate to the Famous Pen Shop in New York. You have enough to buy one of these three pens. Which one would you buy, and how much change should you get?

Notes:

After students choose which pen they will buy, they choose a color for the money spent and shade the appropriate number of boxes on the hundreds grid (see below). The remaining boxes are shaded in using a different color so that the change and money spent are graphically shown.

Encourage students to use their knowledge of tens and ones to determine the amount of change. Discuss how to count units (boxes) to the next greater ten, and then count by tens to one hundred. (see example) Change of a Dollar Chart:

Challenge: If you decided to buy two pens, which two would you buy, and how much change would you get for your \$1?

Challenge 2: How much change would you get if you bought all three pens?

Super extra challenge: If you bought two of each of the pens, and paid with a \$5 bill that your Aunt Betty gave you, how much change would you get?