MULTIPLICATION TRICKS - Danger!

Joy in the Morning: MULTIPLICATION TRICKS

Loni a homeschooling mom of nine kids is going down a treacherous path.

We bought some cheap multiplication math books, and I taped a sheet of paper at the front of each, with tricks, poems, and cartoons of ways to get them to remember these!

I found most of these at Multiplication.Com. One of my favorites is learning the 9's table:

The NINE multiplication fastest is the one less = nine method
Subtract one from the number you are multiplying by. 9 x 5 (One less than 5 is 4)
The first number in the answer is 4. The two numbers that make up the answer will equal 9. So 4 + __ = 9 (5)
The last number in the answer is 5

9 x 5 = 45
One less than 5 is 4 (45)
The answer adds up to nine. 4 + 5 =9

Tricks like this frustrate me to no end. The intentions are well meaning, but the results can be horrible.

My 6th grader was able to get through 3rd grade by using multiplication table tricks like this, but the problem is that she relied to much on them. Multiplication tables should be learned to mastery, and here is why:

Multi-digit multiplication: When performing problems such as 456 x 35, knowing your multiplication facts to mastery reduces your reliance on working memory, which in turn allows you to use your working memory to perform the carrying and adding functions in the standard algorithms. The more things you have to juggle in your working memory, the more likely you are to forget a step and end up with a mistake in a several step problem.

Division: Not only should you know that 6 x 7 = 42, but if given the number 42, you should be able to recall that its the same as "6 x 7". Unfortunately the 9's trick that is used above doesn't work backwards. If given the problem 54 divided by 9, you can not easily reverse the procedure. The problem becomes even worse if you have a problem like 56 divided by 9.

Factoring: Factoring is a key component to algebra. Factoring relies on being able to quickly recognizing multiplication facts and breaking the number down into smaller products. Once again the tricks do no work backwards.

If Loni really wants to help her kids then she will skip the shortcuts and drill her kids over and over till they can spit the facts out like they can their names.

At our house, we use flash cards. Every child in our house is tested on their multiplication tables at least once a day. We also practice doing reverse multiplication tables. The kids are shown the answer, and have to spit out all the multiplication facts that make up that number.

Last year our 6th grader had to get tutoring for her math. Since then I have re-taught her tables, and on her last interim report in math, she was getting a 91.

Don't be fooled people, some knowledge needs to be committed to memory, and hard work is required.

Update: Rightwingprof has corrected me and pointed out that the trick does work backwards... but a child would have to know all the multiples of 9's to know when to use it, and if they did... then they probably wouldn't need to.