Math Fails 2020 Set #6 – using #mathfails to create mathematical discourse.

Hello Friends – Believe it or not, it is that time of year (beginning of August) when I post my yearly set of #mathfails. Thank you to the #MTBoS community for continuig to tag me in your finds. This year’s set has over 100 new images for you to use in your classroom. At the bottom of this post you can find links to sets numbered 1-5.

My favorite way to use #mathfails is to post them in the hallway outside my classroom with a sign saying ‘Can you find the #mathfail?’ or ‘Math Wall of Shame’ and watch all year as it is a continual source of enjoyment for students and adults. Nothing creates discourse around mathematics like a #mathfail. (NOTE: I wrote this paragraph before the start of the pandemic and distance learning. At the end of this post I address how I would use #mathfails during our current state of education)

My second favorite way to use #mathfails is in my classroom to engage students in discourse. Here are several ways I would use images from this year’s set to engage students in discourse.

IS IT A MATH FAIL? …or just a typo…

What is a #mathfail? The definition I’ve used to curate a large number of #mathfails in the last 6 years is ‘a mathematical error based on a misconception’. Often #mathfails are created by using in inaccurate representation of the numerical value or it happens due to a miscalculation. If I am honest – in the set of over 500 #mathfails I’ve collected – my guess is several – particularly those from stores are typos and not created because the creator struggled with a mathematical calculation or concept.

I think using photos that skirt this edge of #mathfail and typo are great for creating discourse.

Denis Sheeran posted the following image on twitter during Thanksgiving 2019. Take a look at his photo and select one of the following statements from the orange box.

  1. The image below is a #mathfail (a mathematical error, misconception)
  2. The error below is simply a typo, a mistake – perhaps the person making this was working too quickly.
  3. There is nothing wrong with this sign. It is correct.
  4. The ‘save 1.00’ represents poor communication.

Here is another image. Is it a #mathfail or an honest mistake?

How could you use this image to create mathematical discourse? I see opportunities for proportional reasoning. What is the cost per ounce? What is the cost per pound? If the 6 oz portion is really $5.99, what should be the cost per pound? If the cost per pound is really $95.84, what would be the cost of a 6 oz portion? ….etc…etc….

Is this a math fail? Part 2. from March 2020 (Shelter in Place time)

This one was posted by MN math leader Ben Orlin. (Thanks Martin Joyce for tagging me) during the need for blood during the beginning of the COVID-19 shelter in place era. I love what Dan Finkel suggested via twitter – this is where the discourse comes in…


Is this a math fail? Part 3. from March 2020 (Shelter in Place time)

Jessica Strom (another MN rock-star math leader) sent me this one during the beginning weeks of our time locked away in our homes in March. This was the time math was featured everywhere in the news (flatten the curve, growing exponentially….). This graph is great for discourse in your students. Why or why not?


Check out the graphs at the world meters Coronavirus page.

CAUTION: The content of this graph may trigger some students, so think about the timing of using it.

Is this a math fail? Part 4. from Late April/Early May (during the stay-at-home era of the pandemic)

In Late April 2020, news stories turned to talking about what it would take to reopen schools. During this time, the CDC released guidelines for what that might look like.

What size would a classroom or a school need to be to assure students have the space they need to be six feet apart at all times?

IS IT A MATH FAIL? …or are we centering USA notation?

Take a look at this pic I was tagged in with the #mathfail hashtag. Is this a ‘math fail’?


If you look closely at the measurements of this drop cloth, you will see an interesting conversion. Eight feet is equivalent to Two thousand four hundred thirty eight meters! What! There is no way that a measurement 2 feet taller than myself can be the same as more than 2 thousand meter sticks. If so – this drop cloth, when opened, would cover _________________, much, much larger than a typical sized room in our American houses. This is a great problem for discourse. If this drop cloth really is 2,348 meters by 3,657 meters (or 8,915,766 square meters) – what size space would it cover.

But wait….perhaps the labeled measurements are correct and I am reading them wrong.

2,438 m in most of the world is 2.438 meters where I live.

This could be a great photo for opening up your student’s world past what we consider ‘normal’ in the US.

Empowering Students – Discourse in the community.


The #mathfail to the right came from my home state and my friend, Greta Bergman. Greta spotted this sign at her local Sam’s Club. What I love about this math fail is that Greta heard from a student’s parent that he was going to offer up ONE PENNY to pay for the sundae. Greta’s twitter thread said that the student ‘convinced management’ to give them a Sundae for a penny using their mathematical reasoning and communication skills. So empowering for students to see math at work. Love it! Would you be bold enough to do what this student did?

Here is another Greta Bergman find from February 2020 at a Target in MN

Everything is exactly $1.00

Greta had posted the same signage from Target in 2017. Still no changes in Target’s future. I loved how the #MTBoS community responded. This would be a great visual as you begin talking about inequalities.


Article: Decimal point error costs Catalina Foothills School District nearly $2 million

POSTSCRIPT – CHANGE CAN HAPPEN (way to go Denis Sheeran & Harry & David)

For the last several years Denis Sheeran has been on a #snowflakesarehexagons rampage during the holiday season – tagging companies on Twitter who are using non-6 sided snowflakes in their advertising and design. Last year (see #mathfail set #5) Denis went after Harry & David (the company) for thier misuse of snowflakes. Check out what happened this year… CLICK to read the thread of comments.

IMAGES speak words

The images we select to represent words matter. These images are great for the “What do you notice?” “What do you wonder?” routine.


Love this one for next Valentine’s Day. Yes Molly!

Is Zero Negative?

Laura Wagenman and Annie Forest both posted pics like this in January. What a great question and chance for discourse with students. Is zero negative? Why would the phone app do this if not? Could the temperature perhaps be -0.5 degrees and it rounded up?

#UnitChat discourse

This #mathfail image comes from my friend Molly Daley from Washington State. Molly posted it as an interesting #unitchat pic, but I think it would make a great #mathfail to inspire mathematical discourse. Check out Molly’s tweet.

Check out the hashtag #UnitChat on twitter for more great ways to add discourse.



Posted January 27, 2020 during Trump’s Impeachment Trial in Senate


Oh Stanford University!

March 2020, during the time CORONA-19 shut down the NBA and all schools across America, Stanford grads started receiving a magazine that includes this add. Do you spot the problem?

My favorite COVID-19 era #mathfail

This image was first shared in March 2020 from locations all over the world as signs posted to remind us to ‘socially distance’. This image needs to be part of all Geometry classes this fall. If you teach 8th grade and will introduce the Pythagorean Theorem this fall – then this fail is for you. Give your students the challenge to ‘Fix this Fail’ and make a new sign for us to display outside.

Update August 2020 – I love that Chrissy Newell is ‘Fixing’ these signs in her sphere of influence! Check it out.

I also love Benjamin Dickman’s extentions to this sign…

Billions and Millions

Super Tuesday in March saw Michael Bloomberg drop out of the democratic presidential race and it brought us another #mathfail.  It all started with this tweet…

Then came the ‘saddest clip in tv’ from Brian Williams on MSNBC commenting on this tweet.

You can see a whole article on the clip HERE.


Rectangles and Squares – Via a 1st Grade Textbook

Dr Kate Owens got us thinking about preciseness in our mathematical definitions in March of 2020. Check out her tweets about the definition of a ‘rectangle’.

More with ‘Squares’

This is the newest math fail in my collection from Lauren Johnson. Is this a fail? Why or Why not?


Is it a square if you don’t include the zipper portion of the bag? Perhaps you could get out a bunch of bags and investigate.

The NY Times Crossword has a #mathfail

The May 13, 2020 NYT Crossword had a mathy clue for row 50a

CLUE 50A: 1, 1, 2, 3, 5, 8, 13, 21, etc…

You can read about the solution to this puzzle HERE. FIBONACCI SERIES

Scaling & Place Value Fail

There are lots and lots of #graphfails in my 6 years of collecting #mathfails. This one found by Amie Albrecht is a new favorite for discourse. This fail has a really common math misconception related to place value. Show your students this graph and ask, ‘What do you notice?’ and start a discussion as a bell ringer some day.

UGH – this might be one of the worst. Check out the horizontal scale.

The state of Georgia’s Department of Public Health released this graph on their website May 2020. So many things are wrong with this. Yikes.


The original tweet with this graphic has been taken down, BUT comments to it are still up FOUND HERE in the thread to the original post..

The thread had many users who changed the graph above to look better. Here is a favorite. It may be a great “What is the same? What is Different?” graph pared with the #mathfail graph. The possible discourse has the potential for empowering students to create graphs that communicate accurate information.


Fixing TURDs

My friend, Christopher Danielson, coined the term ‘T.U.R.D’ for ‘Truly Unfortunate Representations of Data’ at his website years ago. During the Pandemic Era it has resurfaced online in the #MTBoS due to all the graph fails. If you love #mathfails – then also look out for #TURDs online. I love that Andrew Gael will be putting together a ‘Fix That Graph’ unit for his students. Think of all the great discourse that could happen in a unit like this.

Line of Best Fit???

If you are teaching a unit/standards on ‘Lines of Best Fit’ – Check out this graph. In fact check out the entire Twitter Thread below and look at the source and all the comments that would deepen your student’s exploration of this graph. Amazingly bad…

The Twitter Thread above is full of other cool stuff like this MEME…


What is the Same? What is Different?

Image may contain: 1 person, text

July 2, 2020

July 17, 2020

This is my most recent #mathfail for Set #6. It is another COVID-19 #mathfail. This one is perfect for the ‘What is the same? What is different’ math routine. Asking students to discuss the differences is a safe way to foster discourse. These 2 graphs have the potential to talk about data manipulation and the how mathematics can be used within a political agenda.

How to use #mathfails in Distance Learning

I can’t end this blog without addressing the BIGGEST educational paradigm shift in our lives….the pandemic and the move to Distance Learning. Many places this fall will start school with distance learning as part or all of a students learning experience.

My favorite way to use math fails is to display them in the hallway outside my classroom. If I’m not in my classroom, what will this look like? I would be using #mathfails in a variety of ways…

  • I would be making a VIRTUAL Hallway using google slides or a free website or….perhaps I would delve into a ‘bitmoji classroom’ type of thing. I would hang up many of the math fails from the last 6 years so I can have a ongoing display of #mathfails I can reference.
  • Asking students to identify why something is a #mathfail is a safer question for most students. Rather than having to talk about their own mistakes, talking about mistakes of others invites more students into the discussion. For this reason, I would use one #mathfail each week (Maybe #mathfail Friday) and have students write about the math fail.
  • I would use #mathfails as starters synchronously in an online class. I would have it displayed as students are signing on – giving them something to do as others join us.
  • I would make #mathfails part of asynchrounous Choice Boards. (note: I don’t think you can do enough things that give choice to students during this time) Students could select a #mathfail from your virtual #mathfail hallway (number the math fails) and write about why it is a fail or why they like this fail or how one could fix the fail or have them record and upload a video talking about the fail. PRO TIP – Create an expemplar an annotated #mathfail visual with a short paragraph describing the fail and how to fix it to model for students what their work could look like.


You can find my previous 5 sets of Math Fails at the links below.

Set #5 – new summer 2019 112+ images

Set #4 – new summer 2018 87+ images

Set #3 – new summer 2017  93+ images

Set #2 – new summer 2016  72+ images

Set #1 – the Originals collected on or before January 2016  80+ images

To download the 2020 set (#6) of over 100 new math fails, press the orange button below.

Sara VanDerWerf

I am Sara Van Der Werf, a 24-year mathematics teacher in Minneapolis Public Schools. I have taught math in grades 7-12 as well as spent several years leading mathematics at the district office. I currently teach Advanced Algebra at South High School and I'm also the current President of the Minnesota Council of Teachers of Mathematics (MCTM). I am passionate about encouraging and connecting with mathematics teachers. I'd love to connect via twitter.  Join the community.  Tweet me @saravdwerf.

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