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Repeated Addition and Multiplication
Students will be able to use repeated addition as a strategy to multiply two single-digit factors.
- Draw two circles on the board with five dots in each. Ask students what addition problem you’ve drawn (5 + 5). Write the addition problem on the board.
- Review the term repeated addition and explain: Each of these circles have five dots, so we are adding the same number twice. This is called repeated addition because we are adding the same number, or equal groups, repeatedly.
- Connect to multiplication and explain, "Multiplication is another way to add equal groups. So, when we see an addition problem with equal groups, like this one, we can also think of it as a multiplication problem. We have two equal groups of five, so two times five is equal to 5 + 5."
- Tell students, "Today we are going to practice using repeated addition as a strategy to multiply."
Explicit instruction/Teacher modeling(7 minutes)
- On the board, draw four cookies with three chocolate chips in each (4 groups of 3).
- Give context by telling students that someone made cookies with three chocolate chips in each.
- Explain, "In this problem, we need to add the number 3 (write 3 under each cookie on the board) 4 times (emphasize by counting aloud how many cookies there are) to find the total number of chocolate chips. So, we have 4 groups of 3."
- Write a repeated addition expression (3 + 3 + 3 + 3).
- Ask a student to solve (12 chocolate chips).
- Remind students that when we are adding the same number repeatedly, then we can use multiplication. Write a multiplication equation (4 x 3 = 12) and say, "4 groups of 3 is 12."
- Draw another model (5 x 4) on the board.
- Ask students to talk with a partner and come up with an addition expression. Call on a student and write the expression as repeated addition on the board (4 + 4 + 4 + 4 + 4).
- Ask students to talk with a partner and come up with a multiplication expression. Call on a student and write the expression as multiplication on the board (5 x 4). Read the problem as "5 groups of 4."
- Call on a student for a solution and write the answer on the board.
Guided practice/Interactive modeling(25 minutes)
- Play the On a Roll with Multiplication game.
- Model this game for students by rolling two dice. Create a model using the numbers on the dice. Lay out paper plates for the number of groups and place linker cubes on each plate. For example, if you rolled 2 and 6, you would lay out two plates and place six linker cubes on each plate.
- Then, on a sheet of paper write a repeated addition equation and a multiplication equation to go with the model you built (i.e. 6 + 6 = 12 and 2 x 6 = 12)
- Hand out six paper plates, two dice, 36 linker cubes, and a sheet of paper to each pair of students.
- Write the rules of the game on the board for student reference:
- 1) One partner rolls a die to decide how many groups there will be, 2) the other partner rolls to decide how many will be in each group, 3) as a team build a model, 4) write an addition and multiplication problem to go with the model.
- Instruct students to build four or more problems with their partner. (Note: Have students number their problems on their paper as they record so that you can see how many models they have built.)
Independent working time(15 minutes)
- Hand out the Repeated Addition worksheet.
- Instruct students to complete the worksheet independently.
- Circulate and offer support as needed.
- Review the worksheet as a class.
- Provide pre-drawn models and ask students to write a repeated addition problem to go with the model.
- Provide a repeated addition problem and ask students to write it as a multiplication problem.
- During the dice game (On a Roll with Multiplication), have students roll two dice to determine how many linker cubes to place inside each group. This will increase the size of factors up to 12. (Note: in this scenario, students will need 72 linker cubes or other manipulative, like dry beans or macaroni).
- Hand out a sticky note to each student.
- Draw a model on the board and have students write a repeated addition problem and a multiplication problem with a solution on their sticky note.
- Collect student responses as an exit card and check for understanding.
Review and closing(5 minutes)
- Play the repeated addition song to your students.
- Ask students to come up with repeated addition and multiplication problems to go with the song (i.e. 2 eggs + 2 eggs = 4 eggs; 3 flapjacks + 3 flapjacks = 6 flapjacks).