More Multiplication Mastery

Here’s another way to reinforce multiplication concepts with your elementary school kids. You just need a hundreds table and some markers. You can present it like a puzzle. Or you can be fancy and tell your kids that they’re going to make the  Sieve of Eratosthenes.  Yes, that will get their attention.

Here’s the quickie info:

  1. Print this hundreds chart.
  2. Get a handful of markers.
  3. Tell your child that 1 is a special number and gets to be circled right from the start. Let her choose a color to circle it with.
  4. Next tell your child that 2 is also a special number and gets to be circled. Choose any color. Isn’t this exciting?
  5. Now tell your child to cross out any number in the chart that is a multiple of 2. Bye-bye even numbers! (Except for 2, which is circled.)
  6. Next tell your child to circle 3, then cross out all the multiples of 3.
  7. Now tell your child to circle 4…wait! You cannot circle 4 because it has already been crossed out (even number), so circle the next available number…5. Then cross out all multiples of 5.
  8. Continue like this until all numbers in the hundreds table have either been circled or crossed out. There will be 26 circled numbers (25 prime numbers, and 1 – which is not prime.) IMG_2070

Okay, having read the quickie directions, here are some tips to round this out. When I did this with my 9-year-old 3rd-grader, I sat at the table with him. It was lunchtime and we had already been debating a mathy issue. (He insisted that his teacher told him multiplying 0 by 0 was not allowed. I disagreed.) Since he was already in a calm mathy mood, I pulled out a hundreds table. (Yes, I do have them pre-printed and lying around. Don’t you?) I gave him the markers. I started the instructions. I also played around with vocabulary, because how you ask a question determines how the question is understood. When I said, “Cross out all the multiples of 2,” I also said,”Cross out all the numbers 2 can divide evenly into,” and “Cross out all the even numbers.” When I said, “Cross out all the multiples of 3,” I may have actually said, “Cross out all the numbers that you can multiply 3 to get.” I might have even said, “You can just count on from 3, too.” When he finished the 3’s, we paused to note all the numbers that had double cross-outs, i.e. all the numbers that can be divided evenly by both 2 and 3. I also took that opportunity to point this out…if you look at all the numbers that are divisible by 3, you’ll notice that their digits added together give you a number divisible by 3 (ex: take 45…4+5=9, and 9 is divisible by 3.) That’s a neat pattern/trick to know.  Half-way through this activity, my son confused the hundreds table with a multiplication table…they are NOT the same at all. It was helpful that I had a 20×20 multiplication table to show him. You may remember the multiplication table from my post about ditching the multiplication flash cards.

As you sit with your child, observe how he works. Slowly? Excitedly? Does the color of the marker and the precision of his circles and x’s matter to them? Have patience. (Get that cup of tea or coffee that’s always nice to have around when practicing patience.) Ask your child what she notices about the table. Ask your child what she wonders about the table. Observe what gets your child’s attention. Do not get frustrated if he loses attention. Try again another time.

(Mathematically…this activity reinforces multiplication facts without being directly about multiplication facts. As your child works through the table, she might be counting on from each number or adding to each number or actually multiplying each number. Whichever method he is using, he will be working on his facility with numerical manipulation. She will get visual reinforcement of her mental processes. He may notice patterns. She may notice numbers that get crossed out multiple times. In working through the table and observing the colorful work that is created, your child will create new connections to the work. And even though I’ve presented this as a way to reinforce multiplication facts,  it can also be a way to talk about prime numbers and algorithms.)


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