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Fraction Posters N/O vs O/K

Guess what I’m posting today.  Yup.  Another poster.  😀  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.

Fraction Posters Containing Zero N/O vs O/K to Decorate High School or Middle School Math Classroom

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.

N/O Fraction Poster

I made two letter-sized fraction 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.  😀

O/K Fraction Poster

Free Download of N/O and O/K Fraction Posters

Fraction Posters N/O O/K (PDF) (1911 downloads )

Fraction Posters N/O O/K (Editable Publisher File ZIP) (885 downloads )

If you’re interested in editing the file, you will need to download the free font “La unica.”

Want more posters to decorate your math classroom? Check out my posters page!


Sunday 30th of September 2018

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


Monday 19th of November 2018

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.


Wednesday 1st of November 2017

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.


Monday 7th of November 2016

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 :-)


Monday 7th of November 2016

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Monday 4th of January 2016

I made a color version of this at

Sarah Carter (@mathequalslove)

Tuesday 5th of January 2016

Thanks for the link!

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