 # Strategies in Math: Clustering Decimals for Addition or Subtraction

Every few weeks I will receive a question from teachers and parents alike about how to use the strategy of clustering to help with addition and subtraction of decimals. This strategy correlates to the Common Core State Standards for Sixth Grade (6.NS.3) and the Texas Essential Knowledge and Skills Standards for Seventh Grade (7.3 of the new 2014 standards).

Clustering is most simply defined as a bringing together of a close group of numbers. It is important for students to know that clustering decimals can only be done if the set of decimals are centered around the same whole number.

Ex: 7.3 + 6.97 +7.21 =???
You would round each addend to 7 and multiply by 3 to get the estimate of 21 for the answer. When it comes to working further with estimation strategies of decimals, you should also add in Front End Estimation. Both of these strategies are useful when working with decimals and they each have their own place. With this flippable students are able to not only keep track of the steps to follow with each but an example for each as well. Each of these strategies are useful for addition as well as subtraction but need to be laid out for students. I would say that I use Front End Estimation a lot when I am working with decimals in the real world because I know that I can round the whole numbers and then go from there. It is definitely a great thing when you are out shopping and you are buying something that is \$2.69 and you want 4 of them but need to make sure you are within budget. One thing I added to this Interactive Notebook lesson was the reflection word problem. I wanted students to choose from the strategies to determine the appropriate one for finding their solution on top of actually solving the problem. As well as choosing their strategy I wanted them to give reasoning behind why they made that choice. This lesson for Adding and Subtracting Decimals is available in my 6th Grade Number System Unit, 6th Grade Math Interactive Notebook Bundle and 7th Grade Math Interactive Notebook Bundle.

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