My school doesn’t cover interval notation in its curriculum. We focus primarily on inequality notation, although I tend to use the more specific set-builder notation. Each representation has its merits, so I wanted to include interval notation more this year, as an occasional aside. I’ve made a poster (8.5×14) that I’m going to hang up in my room to help students see the connections between the inequality symbols, the choice of open/closed points on a number-line, and the choice of soft/hard brackets in the interval notation. I’ve also made a color-coded version where students can ask themselves, “Can I include this point?” Green=”yes, include”, and red=”no, exclude.” Half of my classes this year are geared toward students who had received <40% in their last math class, so I’m hoping that the stop-light colors can make this yes/no, include/exclude concept easier to grasp. [NOTE: Thanks to lovely conversations on Twitter, it’s been noted that the green/red combination could potentially be dangerous if you have any colorblind students! I’m working on another, more color-friendly version that you can use, as well. I will update this post when it’s been made!]

Before I hang the laminated poster up (I add posters throughout the year as topics arise), I’m going to print another one and cut up the grid into the 36 individual rectangles and hand one piece to each student in my class (if there are fewer students, ask your class “who wants another piece?”–I always seem to have a bunch of volunteers because this means they’ll get to talk to more people!). Students will then find the two other classmates who have representations equivalent to their own card. Once a triple has been found, students will check their cards with the teacher. If they are correct, they will move around the class helping the remaining students. If they are incorrect, they will review which card(s) in their triple didn’t belong as a group of three, and then go back to finding the equivalent representations.

Would you like a copy of the reference poster? Get the color and the black and white versions here! (It’s free!)