Saturday, December 3, 2011

36 club Multiplication Facts

It's been a while since I started posting tips for the 36 club.  I've been working with my youngest on multiplication so I thought I'd post on the subject while it's fresh in my mind.

Since multiplication is more complicated than adding, it's important to make sure they understand the concept behind it.  A fun way to teach this is to bake cookies.

 Show the child you have four rows and three columns. 

They have four sets of three cookies or

 three sets of four cookies. I like to call 3 X 4 the cookie problem.

Once they understand the concept, start with the twos. (I'm not posting ones, tens, or zeros because they're easy to explain.) They already know their addition facts.  Explain that when they are multiplying by two they are adding doubles. So 6 X 2 is the same as 6 + 6.

Next you have the threes.  This is where skip counting comes in.  They should already know how to count by 2's and 5's.  When teaching skip counting, put the numbers to a song.  Try the melody to Twinkle Twinkle Little star for 3's and Row Row Row Your Boat for the 4's. Once they have the songs down, show them how to count off with their fingers.

 This will take care of the 3's and 4's.

Kids can learn to multiply 5s by skip counting, but eventually, they need to speed things up.  All they half to do is cut the number is half.  So, for 6 X 5. Half of 6 is 3.  Put a zero on the end.  That's the answer.  For odd numbers, it doesn't half evenly, so they will have a 5 at the end instead of zero. So, for 5 X 7, half of 7 is 3.5. 5 X 7 is 35.

 My kids have a hard time remembering the skip counting for 6,7, and 8 so I went for a different approach. But first I'll skip to 9.  I think most people know this but I'm posting it anyway just in case.  Have the child hold up their hands when they are multiplying a number by 9. Count the number of fingers they are multiplying nine by and put that finger down.  My example below is for multiplying by six.  The answer to the problem is in the number of fingers left up.

This leaves us with higher numbers. 6X6, 6X7, 6X8, 7X7, 7X8, and 8X8

For 6X6 and 6X8, have the child count by fives first. This goes back to adding sets of numbers.  So first they have to figure out how many 5 sets of 6 equals.  Then they just have to add one more set. So five sets of six is 30. Then they add one more set of six for 36.  It also helps to point out that even numbers multiplied by six end in that number so when they say the complete fact out loud it rhymes.

My daughter learned a poem for 7 X 7: Seven and seven went to heaven to see the 49ers.
I added to it to help with 6 X 7.: 6 lost a shoe and only got 42. (No it doesn't make sense.  But the rhyming helps anyway.)
My son insisted I come up with one for 8 X 8: Eight and eight slipped on the floor.  How many stiches? 64.
The last one is the easiest.  7 X 8.  They're in order. 7 - 8.  The answer is in order too.  5 - 6. So it counts.  56 =7*8 (5,6,7,8)

One more tip for multiplying even numbers.  If they get stuck when multiplying any even number, all they have to do is cut the number in half, multiply, and then double the answer.  For example: 8X4. You could cut either number in half. Half of 8 is 4. 4X4 is 16. 16 +16 is 32. (8x4=32) Or you could cut the 4 in half. 8X2 is 16. 16 +16 = 32.  (I can't do that math problem without the inchworm song getting stuck in my head.  Click the link.  You know you want to.) My son has a hard time remembering 6X7, despite my genius poem.  Now he cuts 6 in half (3), multiplies that by 7 (21) then doubles the answer. (42)

And that covers all 36 facts.  It is important to practice the facts with the kids every day.  I time them and let them stop as soon as they beat their old time.  After a while they start remembering them without all the tricks.  My son's multiplication time is 4.5 min.  We've been working on these for about a month. I still have to remind him of the tips while we go through the cards but he remembers most of them on his own.

*Update.  It's been a few years since I first posted this blog.  My son is now in 3rd grade and his multiplication time is down to 1:41. (So close!)  His second grade teacher didn't do 36 club so he got rusty. We're still learning as we go so I added tips on cutting numbers in half.

Addition Tips
Subtraction Tips
Division Tips
Humdinger tips

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