# WODB: Which One Doesn’t Belong?

Today, I just want to write a quick post about a #MTBoS resource that I hope everyone is already familiar with. I used it a couple of weeks ago in my classroom, and the experience was such a fun, positive one!

The resource is Which One Doesn’t Belong?

The idea is that there are four pictures. Each of the pictures could be the answer to Which One Doesn’t Belong? Your job is to find a reason why each picture doesn’t belong.

I used this as one of my Figure It Out! Fridays a little while back. I tossed this picture up on the SMART Board and asked “Which One Doesn’t Belong? “

I intentionally didn’t tell them at first that each one of them had a reason it didn’t belong. Instead, I let one student claim that the shaded square didn’t belong. Another student claimed that the pentagon didn’t belong. I stood there and watched them start to argue it out before stepping in and saying that there was actually a reason why each of them didn’t belong. The bottom right shape gave my students the most trouble. This was a great exercise in practicing precision with our vocabulary and explanations!

After we found a reason for each one, I tried to move on to our lesson of the day, but students protested. They wanted to do another! So, I ended up putting this one on the screen, too.

As the day progressed, it was interesting to see the different reasons different classes came up with fo a card not belonging! I like how this promotes critical thinking, thinking outside the box, and justifying your answer.

You can find plenty of these puzzles at WODB.CA. They are broken into three categories: shapes, numbers, and graphs.

Here is a sequence completion puzzle/game that has a similar philosophical spirit to WODB, from one of Denise Gaskin's post: math with many right answers

Of course, the idea of extending a sequence in different ways is not novel, but, in practice, I often find it hard to come up with satisfying justifications. The examples in the post are really helpful.

I like this idea! Thanks for the link!

I was literally visiting your blog this afternoon to find links for "Which One Doesn't Belong?" and I'm so happy you wrote this post to make me search easier. 🙂

I plan on using these as warm-ups for my Algebra 2, Algebra 1, and Geometry students. I'm hoping that it generates some good conversation.

Ha ha – perfect timing!

I'm looking for WODB pictures for kindergarten. Any suggestions?

Dot cards, addends for 5 or not 5,