by C. Elkins, OK Math and Reading Lady
In part 2, I will show you some ways to help students decompose a multiplication problem into 2 (or more) easier multiplication problems. Most students know problems with factors of 2, 5, and 10. The decomposing will allow students to use what they know to work on the unknown / unmemorized fact.
I frequently see students struggle with solving an unknown multiplication problem. Often they choose skip counting, but if they miss just one number in the sequence, the answer comes out wrong. I also see them use their multiplication chart, but this doesn’t do much to help them apply number sense. Other times I see students draw circles with dots inside, but this is time consuming and it often becomes just a counting practice. This method is using the distributive property. Students can break apart one of the factors into “friendly” addends. I usually advise making one of the addends a 2, 5, or 10 since those are usually easier to compute or are already memorized. Here are some examples:
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- 8 x 6 = (8×5) + (8×1)
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- 7 x 8 = (7×5) + (7×3)
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- 4 x 12 = (4×10) + (4×2)
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- 6 x 6 = (6×2) + (6×2) + (6×2)
I have also attached a class activity sheet in which students cut out grids, glue them on the worksheet and then decompose them. Get it free here: Distributive property teaching chart Another resource for teachers is my multiplication strategies guide which shows some ways to break down each factor’s family. Get it here free: Multiplication fact strategies chart Finally, here is a link to a TPT source with a freebie for using the distributive property with arrays: Distrib. Property of Multip. freebie by Tonya’s Treats for Teachers
Have a great Spring Break for Oklahoma teachers!! I will be back in 2 weeks with more multiplication strategies.
Thank you for publishing this information about distributing (decomposing) various problems. I appreciate the visuals – helps me understand the importance of providing the same to students when teaching or reviewing concepts.
Rob
RobertC@ckschools.org
Thank you, Rob. I appreciate your message. In case you haven’t used this link before (mathlearningcenter.org/apps), check out the virtual geoboard. You can adjust the geoboard to make a 5×5 grid (or larger when using the tools). This is a great tool to use with the strategy I mentioned. You can show a different color for sections of your grid to highlight use of the distributive property – – instead of drawing it. You can also use the writing tools to write on it. Check it out! Have a great week!