Wednesday, October 16, 2013

Cluster Problems for Multi-Digit Multiplication

True story: Several years ago (when I was still a third grade teacher), I was in a fourth grade math teacher's classroom for an Early Release meeting.  When I'm in other teachers' classrooms, I like to scan the walls for charts and other visuals I can recreate and use with my students.  I distinctly remember seeing the words "cluster problems" in this teacher's room on a chart as a multiplication strategy.  Cluster problems?!  I thought to myself.  What are cluster problems?  I've never even heard of those! Reason #120 to keep me in third grade math. 

Well, fast forward a few years, and now I am a fourth grade math teacher who is responsible for teaching her students how to multiply greater numbers using new strategies such as...cluster problems!  After reading (more like studying!) the teacher's edition for the lesson introducing cluster problems no less than three times, I bypassed Google for help and went straight to YouTube! 



Our benchmark for fourth grade multiplication goes up to four digits times two digits, so we will use cluster problems when appropriate.  When using cluster problems to solve a multi-digit multiplication problem, it is important to discuss how the cluster problems are related to the "final problem".  In other words, how can using a combination of cluster problems help solve a more challenging problem?

As students become more comfortable with this strategy, they will create their own cluster problems to solve a final problem.  When creating your own cluster problems, some things to think about may include:
  • How can I break apart one factor by its place value?
  • How can I break apart one factor in another way?  What landmark multiple(s) can I use to solve this problem? (Landmark multiples are 10, 5, 20 times a number.  They can be used to help you get close to the number you're multiplying more quickly.)
  • Can I half one factor, then double the product?
  • Can I half one factor (I recommend the one that's greater) and double the other factor to create an equivalent problem?

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