Monday, October 29, 2007

Adding and Subtracting Integers Card Game

Last year my students had their usual struggles with adding and subtracting integers at the beginning of the year (this is not just a middle school problem). So I used a game I found online called Twenty Five, where students would draw from a regular deck of cards and add them to a pile, trying to reach a target sum of 25. Red cards were negative and black cards were positive, and each new card would be added to all the ones put on the pile before it. Presumably students were writing down each addition problem they did. It was a waste of time: it was hard to monitor whether students were adding correctly during the game, and difficult for students to keep track of and add up 10, 15 or 20 numbers quickly.

Since then I have been laboring over an idea for my own game, since I believe this would help my students internalize an essential skill. I came up with a complete game, but it was too complicated for classroom use (based on my experience with Like Terms); too many rules and steps to get caught up in would leave the core activity lost in the fray. It could be suited for an advanced class, block schedule or playing at home. In a regular 45-55 minute class, things need to be simpler.

I actually eschewed any game this year and focused on the number line as a simpler tool for students to use to add and subtract integers correctly. What dawned on me last weekend was that the number line was the missing piece to the puzzle. Here now, for the first time ever, is Plus/Minus.

  1. Standard 52-card deck of playing cards
  2. Paper and pencils.
  3. 2 objects to mark a goal and starting location
  1. Students draw a number line on a piece of paper, at least from -10 to 10 with room for more.
  2. Have 2 objects (maybe candy the winner can eat afterwards?) to mark the location of the goal and the current location of the players
  3. No cards are dealt. There is a face down draw pile and face up pile for each card drawn.
Game Play
  1. Flip the top card from the draw pile. This is the goal. Black card are positive whole numbers and red cards are negative (aces are 1 and all other face cards are 10). The starting point is zero.
  2. Each student takes a turn flipping the next card from the draw pile. They add that number to 0 and move to the resulting location. If they reach the goal number, they win. If not, their turn is over and each player takes a turn moving back and forth on the number line until someone reaches the goal.
  3. After one or several games (depending on time) , switch to subtracting all numbers.
While They Play

Students must write down each simple addition or subtraction problem they are doing throughout each game. This is what you can check and grade immediately as you are monitoring the game. Follow up with homework for practice.


At the end of this lesson, use a mini-poster where students have to show an example, write out how to do it (what the rule is) and most importantly include the correct answer. Hang the best ones up on the wall (as you should always do with good examples of student work).

When To Play

This would be a good game to play after a day where you had introduced the concepts or when you were reteaching. I think that the number line makes this concept easy to understand with little upfront work, but that is an assumption on my part. Use it whenever you feel it is appropriate.