Math = Love: Killing Cats Poster

Saturday, October 31, 2015

Killing Cats Poster

My Algebra 2 kids are working with rational expressions.  I'm pretty sure it's my least favorite topic to teach in the world.  It's tedious, and it's a nightmare for my students who haven't fully mastered factoring.  My students have traditionally struggled with remembering that they can only cancel factors and not terms.  I started fighting against this a couple of years ago by telling my students that every time they canceled out terms, a kitten died.

Rational Functions - Every time you do this, a kitten dies.

I originally found this on Math Curmudgeon.  There's a whole set of pictures of different animals dying for various common math mistakes.  You should definitely follow the link!

I've blogged about using this in a lesson before here.  

This year, to build anticipation and provoke curiosity, I hung this poster up in my classroom a couple of weeks before our unit on rationals.  Of course, my Algebra 1 kiddos ended up asking the most questions about it, and I had to explain that it was an Algebra 2 thing.  They hate when I tell them that something is for another class.

I make a really big deal whenever someone kills a cat and I have to change the count.  And, the kids are always watching to make sure I accurately update the count each day.

Here's the file if you want to play along.

And, for the record, two cat posts in a row is just a coincidence.  Promise.


  1. I heard Dan Meyer speak yesterday about "If ___ is the aspirin, what is the headache?" If simplifying rational expressions is the aspirin, what is the headache?" He showed 3 rational expressions being added (need a common denominator, factor, etc) and asked why would they need it? Then, it simplified to (x-4)/(x-6). Give the original problem to the kids, ask them to evaluate when x is say 2. Then, you do it after them without showing them you are using the simplified version. They see you are doing it more quickly, more efficiently, which way do they want to do it? Does that make sense?

    1. I read his post about this, but I'd completely forgotten about it. Thanks for the reminder!

    2. I was there, too! And I sat next to Jen! :) And I love the motovation of the cat safety count. I think combining the two wpuld actually make this dreariness not so painful.

    3. My kids even have started updating it themselves!

  2. Love this, Sarah! I may incorporate something like the kitten dying into my unit on parallel lines that we are getting ready to do in geometry. Students always want to say that "If angles are corresponding, then they are congruent" missing the fact that *the lines must be parallel* !!! I've tried all sorts of things over the years to get them to stop making that mistake... maybe a kitten just needs to die in order for them to get the point. :) Thanks for sharing all your ideas... it's such a joy and pleasure to peek inside your classroom on a regular basis. Blessings to you, my dear!

  3. I mentioned a kitten dying to my Alg. 2 class and it worked until one boy said, "I have a large dog and I hate cats, so it doesn't bother me." Ugh. Thanks for sharing your ideas and experiences!

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