Which One Doesn’t Belong?

After all of the interesting conversation around Christopher’s (@trianglemancsd) Shapes Book and a conversation with Faith (@Foizym), I thought it would be fun to take this thought about “Which One Doesn’t Belong” into my students’ decimal work. With these decimals, I wanted to draw out reasonings about closeness to benchmarks, equivalents, and properties of numbers in relation to decimals. It did all of that and more! I wrote the following four decimals on the board and had students talk about which one they thought didn’t belong:

woIn brainstorming these decimals beforehand, I knew that 0.49 would be the most obvious because it is the only one that went into the hundredths, so I go that out of the way as the sample response and asked them to see if they could find another reason for 0.49 or any of the other three decimals. They brought out some pretty great stuff and definitely gave me insight into how they think about multiplication of decimals! It was also so nice to hear, as I walked around during their talk, the freedom students felt expressing their ideas when they knew there was no right or wrong answer!


12 thoughts on “Which One Doesn’t Belong?

  1. Pingback: Properties of Numbers | Math Minds

  2. Marian Dingle

    I tried this with my 3 classes of fifth graders. In all 3 classes, a student commented that 0.49 didn’t belong because it was odd. This led to 3 different rich discussions on the definitions of odd and even, a topic that most had assumed was long gone since second grade. They debated each other, rethought their arguments, tested conjectures…it was awesome! Thank you for sharing this problem.


    1. mathmindsblog Post author

      That is awesome Marian!! Thank you so much for sharing how it went, I love to hear those stories!! It is so crazy to me that I have never thought to revisit even/odd until this year! So much learning around it!



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