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Halves as Fair Shares
Students will be able to divide circles and rectangles into equal parts and identify halves.
- Ask students to give you a thumbs-up if they have ever eaten birthday cake.
- Tell students to imagine a small birthday cake, and draw a circle on the board.
- Say something like, "My friend and I are going to split this birthday cake." Draw a line diagonally across the cake, but do not divide the circle in half.
- Say, "My friend thinks this is a fair way to share the cake." Ask students whether they think the cake is divided equally. Have students explain their thinking, and talk about how they notice that one piece of the circle is bigger than the other.
Explicit Instruction/Teacher modeling(5 minutes)
- Erase the line you drew and have a student volunteer come to the board and divide the cake fairly.
- Explain that the student divided the cake in half. Write "1 half" on each equal part of the circle. Use the word "half" rather than the fraction symbol.
- Think aloud by saying, "Sometimes I have been to birthday parties where the cake is a rectangle instead of a circle." Draw a rectangle on the board.
- Guide students in thinking about ways to divide the rectangle into equal shares. Have a student volunteer come to the board to divide the rectangle in half.
- Acknowledge the student for dividing the rectangle into two equal parts, and label each part "1 half." Ask students to show you by positioning their arms other ways to divide the rectangle in half.
- Draw two more rectangles on the board, and agree that the rectangle could be cut up and down (vertically), back and forth (horizontally), or corner to corner (diagonally). Label the halves.
- Ask students whether they would each get more or less cake after dividing the cake with their friend. Point out that when the cake is divided in half, each person gets a smaller amount.
Guided Practice(5 minutes)
- Create a T-chart titled "Equal and Unequal Parts."
- Show students the images from the Equal/Unequal Parts worksheet examples.
- Have students give you a thumbs-up if the parts are equal and a thumbs-down if the parts are not equal.
- Have students come tape the shape in the appropriate column of the T-chart as you show students the examples.
Independent working time(15 minutes)
- Distribute the Divide the Shape in Half worksheet to the class. After you check that students have correctly divided the shapes, have them color one half of each shape.
- Provide students with more examples and nonexamples of shapes divided into equal parts.
- Pull students to work in a teacher-led small group.
- Have students label each equal part "one half."
- Have students create their own T-chart with examples and nonexamples of shapes divided into equal parts on the back of the worksheet.
- Have students complete the Four Equal Quarters worksheet
- Ask students to explain how they know that the shapes are divided into equal parts.
Review and closing(5 minutes)
- Collect student work and call students back to the rug.
- Show students another example of dividing a whole into two halves by holding up a piece of string.
- Cut the string into unequal parts. Hold both pieces of string up next to one another and ask students to give you a thumbs-up if the parts are equal.
- Cut another piece of string into equal parts. Hold up the pieces so that students see both pieces are the same length.
- Remind students, "I just cut the string in half."