Distribute Fortune Teller Student Handout Gr3-4. Depending on how much experience your students have had with area, review some basic ideas about the meaning of area (the amount of space that a 2-dimensional or flat shape takes up) and square units:

• Unit squares are 1 unit long and 1 unit wide.
• The area of a unit square is 1 square unit.
• Unit squares can be used to measure area of other shapes by placing them next to each other without gaps or overlaps.
• They can represent standard measures, like square inches, square centimeters, or square miles.

Give students several minutes to attempt to find the area of the three shapes on the first page of the handout. Have students share how they found their answers.

• In #2, guide students to recognize that when a square is cut diagonally into two equal parts, each part is ½ of the unit square.
• In #3, guide students to recognize that the two half squares can be put together to make a whole square.

Give students the 8x10 Grid for Making Fortune Teller and ask:

• What is the area of this shape? How do you know?” Encourage students to list several strategies: counting all of the squares, counting by 8s, counting by 10s, multiplying 8 × 10 using known facts, etc. Model any that are unfamiliar.
• Remind students that the Fortune Teller is made from a square and ask them how they can make a square from this rectangle. What is the largest square you can make? (8x8)
• For fourth grade, use this as an opportunity to elicit the properties of a square and a rectangle.
• Have students cut out the 8x8 square and ask them to find the area.
• Again, share strategies for finding the area of the square (64 square units)

Demonstrate (or have a volunteer demonstrate) the first step of making the fortune teller, folding it corner to corner. Have students identify the new shape. For fourth grade, focus on why it is a right triangle.

• What is the area of this new shape? How do you know? Focus on having students justify that the right triangle has half the area of the square. Students can unfold to see that there are two identical copies of the triangle in the square, therefore the triangle has 1/2 the area of the square or 32 square units.

Confirm through other methods that the area of the trianble is 32 square units.  Possible methods include:

• counting all of the squares and putting together 2 half squares to make whole squares
• dividing the space into smaller rectangles and adding them together, then adding extra squares and half squares
• thinking about the triangle as half of the original square and dividing 64 square inches by 2 to get 64 ÷ 2 = 32

Key mathematical terms: area, square units, rectangle, square, right triangle (gr. 4)