Which one doesn't belong math walk

Which One Doesn't Belong is an engaging structure to use on a math walk!

What is it?

Based on Mary Bourassa's site and Christopher Danielson's book!

Which One Doesn't Belong is a set of 4 items (numbers, equations, shapes, graphs...) where each one has something(s) different than the other 3 items. For example:

3 Doesn't belong because it is the only single digit

31 Doesn't belong because it is prime (and not divisible by 3)

123 Doesn't belong because it is the one with consecutive numbers (or 3 digits)

27 Doesn't belong because it is the only one divisible by 9 (and the only one without a 3)

Why is it great?

Accessible for a wide audience band
Creates a math discussion
Values observation
Low anxiety for being "right" since each has a reason (or multiple reasons) for not belonging
You can choose images/numbers that are easily drawn.
You can create one for any level of math

How can I chalk it?

Be sure you have your math walk supplies ready! Choose a good section of sidewalk (smooth, no shadows.) How to tips.
Find a "Which one Doesn't Belong" picture that is easy to draw (or print one to attach to a public bulletin board or pole.) Here is a website with a bunch to choose from. Making your own is even more fun if you have time!
Draw it out on paper (or I use an index card) to help with spacing and decrease mistakes.
Divide the sidewalk into four sections (it helps discussion to label each one with a letter or number- I like to use the coordinate plane roman numerals.) I will sometimes use the index card for the perpendicular center lines.
If you have colors, you can make one a different color (or more than one color) to add to the differences. If using shapes you can add patterns instead of coloring them in.
Take a picture (overhead is best- watch for shadows). Crop the picture and post it on our Facebook Group, Instagram, or Twitter with the hashtag #mathwalk I would love it if you would tag @traciteacher so I can share your great work!