Adding and Subtracting Positive and Negative Integers

By Vicki M. DePountis on Apr 24, 2017

Addition and subtraction of positive and negative integers

Materials

  1. 2 sets of 10-20 visually and tactually different tokens. Several MathBuilders kits, like Unit 1 have textured shapes. Other alternatives are:
    • 20 pennies and 20 quarters
    • 20 Jacks and 20 marbles
    • 20 small felt circles and 20 pennies
    • 2 quadrant work boards.
  2. For visual learners, a large piece of oak tag or card stock, at least 14” x 8,” divided into 2 7” x 8” areas with a thick solid line.
  3. For tactual learners, a work-play tray with a 2 part divider (APH). Cookie sheets and velcro boards work as well and will keep magnetic or velcro tokens in place. Divide with thick glue, pipe-cleaners, a pencil...

Procedure

  1. Using the 2 quadrant work board, have students establish “zero” by asking students how many tokens are on the board. Explain that the right quadrant is the positive quadrant, just like on the number line. The left is the negative, just like on the number line. Establish which tokens will be “positive” and which will be “negative.” Explain that only the positive tokens can go on the right or positive quadrant, and the negatives must go in the left or negative quadrant.
  2. Explain that adding means placing tokens on the board. Have students place a different number positive tokens on the right side. After each placement, ask them the “value” of their board. For example, “Place 7 positive tokens (+7) on the board. What is the value of your board?”
  3. Have students add 5 positive tokens to the 7 tokens on their board. Ask them the value of their board. (+7) + (+5) =
  4. Explain that subtracting means “taking away” from the board. Have students take away various numbers of positive tokens. After each subtraction, ask them the value of their board.
  5. Have students place 7 positive tokens on the board. Ask them to take away or subtract 5 of them. Ask them to subtract another 2. What is the value of their board? (+7) - (+5) - (+2) =
  6. Have students place 5 positive tokens on their board. Have them take away 7 positive tokens .
  7. (+5) - (+7) = Discuss what happens. How can you represent the value? Introduce the negative token. Students will need 2 negative tokens on the left or negative side of the board to represent the value “-2.”
  8. Practice subtracting to a negative result. Make sure they record the mathematical expression and result for each example. Braille readers can pair up with another student. The braille reader can record each problem with slate and stylus on an index card while the student with vision writes the same problem on the back side of the card. (+5) - (+7) = (-2)
  9. Ask students how you might add negative 2 to the board. For example, if they have 5 positive tokens and are told to add 2 negative tokens, what is the total value of the board? If they have 3 positive tokens and are told to add 9 negative tokens, what is the value of the board? +3 + -9 =
  10. Ask students how they might take away -2 from the board:
    • Students will then examine all the problems they have been computing and look for patterns.
    • What happens when you add a positive tokens to another number of positive tokens?
    • What happens when you add a negative tokens to another number of negative tokens? What happens when you are adding positive tokens and negative tokens? When is your total value positive and when is it negative? What happens when you take away positive tokens from positive tokens? What happens if you take away negative tokens from positive tokens? What happens when you take away positive tokens from negative tokens? What happens when you take negative tokens from negative tokens?
** Independent living skills may be addressed when topic is checking accounts. What does using a debit card do? What does getting a refund do?