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14
Sep 2015

Army Men: Adding Negatives

Thanks to Julie R, I started teaching adding integers (my first topic of the year) using army men. The students LOVED it! So here’s how I did it: Setup: Ordered over 100 red and 100 grey army men online. Put 10 grey and 10 red army men into a ziploc baggie for each pair in […]

Thanks to Julie R, I started teaching adding integers (my first topic of the year) using army men. The students LOVED it! So here's how I did it: Setup:
  • Ordered over 100 red and 100 grey army men online.
  • Put 10 grey and 10 red army men into a ziploc baggie for each pair in my class.
The Lesson:
  • Passed out a baggie full of army men (10 red, 10 grey) to each pair
  • Gave students the following rules on a slide:
    • Each partner gets 10 army men of one color.
    • The grey men are called the Positive Army.
    • The red men are called the Negative Army.
    • Partners have to clear a "battlefield" between their army men.
    • Anytime a grey army man meets a red army man on the battlefield, it is a fight to the death.
  • Walked through three examples with them:
    • Starting with "1 + (-1)" I had each partner put one army man onto the battlefield. Since it is a fight to the death, we know there will be 0 men left on the battlefield. Hence 1 + (-1) = 0.
    • We defined this as a zero pair.
    • Then we did "5 + (-2)", discussing what the answer is and why it must be positive.
    • Lastly, we did "7 + 1", where there is no battle (the positive army is just adding reinforcements) because there are no negative army men on the battlefield to fight.
  • Then, I gave the students a dozen adding integers problems to work out. I insisted that they act out the "battles" with their army men.
This was such an awesome hands on lesson, and even though we didn't come back to army men again, the students still brought it up. They knew that 63 + (-80) was going to have a negative answer because there were more negative army men. They also would discuss how 63 army men on both teams will cancel out (subtract). Huge thanks to Julie for the great recommendation!
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