Memorizing the Multiplication Tables to 20 - That's Just Crazy!
Posted: Sunday, November 23, 2008
by Brian Foley
Magic and Learning
Do you have a child who needs a confidence-boost in school? Imagine if your child knew the multiplication tables up to 20. It would make him or her seem like a genius compared to most school children who have problems even remembering 7x 8!
If you are like most people, you probably think that memorizing the times tables to twenty would be a heck of a chore. It would! It would be crazy!
Here's how you do it:
Let's say you are multiplying 12 x 17.
Step 1) Add the ones column of either of those numbers to the other number. In this case you could add either 7 + 12 or 2 + 17. (Both would give you the same result, namely 19). Put a zero after it, to get 190.
Step 2) Get the product of the last digits of each of the original numbers (that would be 2 x 7, which would give you 14).
Step 3) Add the two numbers you got. In this case that would be 190 + 14. You'd get 204, and you'd be done, because 12 x 17 = 204.
That's how easy it is, and it works for any numbers between 10 and 20!
Try 19 x 14.
1) 19 + 4 = 23. 23 with a zero at the end is 230.
2) 9 x 4 =36
3) 230 + 36 = 266, which is the correct answer. Piece of cake!
Please, please, please don't ever write anything down when you do this! It wlll defeat the whole purpose of this method. Writing down things that a child's mind should be able to do is like training yourself to use crutches when you don't need them. The whole point of this is to trust your brain, and learn to do simple math mentally.
Here are some more examples. Once you have practiced them, you should become fast enough to amaze anyone, especially an elementary school teacher. A third-grader should be able to do these with ease in a short time, and become the "Einstein" of his or her class.
18 x 13
15 x 16
19 x 18
17 x 14
12 x 16
You may come across instances where you will have to carry. You will automatically understand how to do that if you pay attention.
Remember, you are trying to boost confidence, and you can't do that unless you have the basics down. With the basic multiplication tables "in your bones," this way to multiply numbers up to 20 can be a "reputation-maker."
Of course, if you or someone you know (your child or student, maybe?) hasn't totally masteredthe "multiplication tables," the above method won't do you much good, will it? You'll be happy to know that there is a fool-proof, easy way to teach or learn the basic times-tables in minutes, and it's even easier than the the method for multiplication of 10 through 20. You can learn about it at Learn to Multiply.
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Top-level comments on this article: (9 total)O my Gosh, you lost me. I tried it and it didn't make sense to me with the written instructions, but I did get it when you wjust used the numbers for 19 x 14.Good job! Unfortunately, I am work in accounts receivable and my brain has relied way too much on my adding machine. You made me work my brain and it felt good. Blessings, Teresa
Hey Brian? Way cool! Thanks!
While subbing I found it totally shocking how many could not do the tables? A blight on our nation. Thanks for the help.
I'm going to put my eight year old son on this right away.
Ummm if you are impressed by this, you really need to check out some books on VEDIC MATHEMATICS from Amazon or some other book store. Vedic Maths is the way Ancient indians (from INDIA) used to do maths and it is full of these kinda short cuts. And not just for simple addition subtraction multiplication division, but even for trignometry and calculus. For example i can do 1 divided by 19 to 14 decimal places in 10 seconds flat using a vedic maths techniquei ve seen many vedic mathematical tricks but for diff mul u need diff tricks .herein only 1 trick applies to all wich lies between 10 to 20.incase u nw sm tricks i would be highly obliged if u cud share it with me n enlighten ma poor mindUmm, The only problem I see with Vedic Maths is that it somehow wants to claim ownership of various techniques. The methods are fine, but not necessarily unique, or Vedic.
As long as people understand that math crosses all cultures and is in no way to be abdicated to any marketing strategy (which is essentially what Vedic Maths is), then by all means learn with Vedic Maths. But be careful that you don't get sucked into to anything but the math itself.
yes its great to have a view like this in maths .........
Thanks a lot for this post.... solved longmy longterm problem in multiplication
ohhh, great post. Thanks for the TIP.
Hey man. Thankx
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