Teaching Through a Math Story
Tell students a math story, such as the following:
“You’re getting ready to go to a party at a friend’s house, and you’re gathering up three cans of soda to bring with you. Your friend, who is putting the party together, asked five of you to bring three cans of soda each. Suddenly, the phone rings. Your friend has realized that there may be more people there than she thought, so she’s asking each of her five friends to bring an additional two cans of soda. You wonder how many more friends she expects to come. How can you find out?"
Students will likely try to figure this out the hard way by first adding together three and two, multiplying times five, to get a result of twenty-five; then they’ll multiply three times five to get ten; and then they’ll subtract ten from twenty-five to get fifteen. Ask them how they would write out the equation for the total number of soda cans, and write it on the board (they should come up with “5(2+3)"). Then explain to them that they can use this equation to come up with the answer to the original question in a much easier way. Divide them into groups and have them work to figure out an answer to the question. Hopefully, they should realize that the equation can be changed to 5*2 + 5*3, so the answer would be 5*3, or 15.
Use the following procedures for teaching the distributive property:
- To help students understand why the distributive property works, use blocks in two different colors, such as red and blue.
- To illustrate what 5(2+3) means, lay out two red blocks and three blue blocks.
- Then lay out an addition four rows of blocks – made of two red blocks and three blue blocks each – and show how there are five rows of two blocks, and five rows of three blocks.
- Give students other expressions that demonstrate distribution over addition, and have students use their own blocks to illustrate each expression.
- Then do the same with expressions that demonstrate distribution over subtraction, such as 5(3-2).
This distributive property lesson plan will help you teach students how to deal with multiplication coupled with addition or subtraction.