Math = Love: Fractions Containing Zero N/O O/K Posters

Thursday, August 6, 2015

Fractions Containing Zero N/O O/K Posters

Guess what I'm posting today.  Yup.  Another poster.  :D  I won't be allowed to start decorating my classroom until late next week, so I've been compensating by making new stuff to decorate it with.

Back in January, Elissa posted her Dividing by Zero? posters that were inspired by this pin.  I decided these had to go in my classroom for the next school year.  I've used the N/O and O/K notation to remind students that it is not okay to divide by zero for a couple of years now.  But, a reminder on the wall is always handy.

I've found that my Algebra 1 students, especially, struggle with seeing the difference between a fraction that is undefined and a fraction that equals zero when working with slope.  It's like they see the zero and automatically assume the answer is zero without thinking about where the zero is in the fraction.

I made two letter-sized posters to remind students that a zero in the numerator is okay, and it equals zero.  A zero in the denominator is a big no-no, and it is undefined.  At first, I was frustrated that the word undefined wouldn't fit.  Then, I got excited that I could write the word vertically since vertical lines have undefined slope.  :D

I've uploaded the posters here as an editable Publisher file (will need to download the font "La unica") and a non-editable PDF file.

Once these are hanging up in my classroom, I'll be sure to update this pot with a picture.  


  1. I made a color version of this at

  2. This comment has been removed by the author.

  3. i just found your site and i just want to say THANK YOU!!! i'm tearing my hair out with my students this semester...i teach a transition-to-college program for adults, and have a lot of struggling math-phobes in my class. usually things go pretty well, but something just isn't clicking for this cohort. i'm SO EXCITED to try some of your ideas! i think they will be AMAZING for my visual learners! i can't believe you are just putting all this out there for free...your hard work is much appreciated, and if you wrote a book i would buy it :-)

  4. You didn’t include a poster showing zero simultaneously in the numerator and denominator as a fraction. That fraction is considered undetermined because you’re not dividing anything at all and therefore have no clue what you might’ve actually started with since any number times zero will equal zero. I guess you either couldn’t make a clever reminder or didn’t know that “zero divided by zero” was (and still is) supposed to be called the undetermined fraction.

  5. Sorry, but N/0 = undefined is WRONG.
    0/0 = undefined (undefined means that any result number works, indeed 0=A*0 for any A)
    3/0 is impossible instead (no result work, indeed 3=A*0 is not true for any number A)

    1. N/O is correct (until you come to calculus), O/K is incorrect as 0/0 is also a no and it isn't apparent if you just have this poster.