Tricks for Learning AdditionDate: 08/17/98 at 21:50:25 From: maria ralston Subject: Learning family facts to 12 I have trouble doing all the addition and subtraction problems that still make me count on my fingers. I lose track of what I am counting if I get distracted. I have not memorized all of them yet. I need help so I won't be slow in math in my 3rd grade. I was in a mixed classroom last year and I got to be a second grader. My mom taught me a little bit of math before I went to school. I love to read and write, but I want to be as good as that in math too. Date: 08/18/98 at 12:56:49 From: Doctor Peterson Subject: Re: Learning family facts to 12 Hi, Maria. I think you can see why it's good to learn those facts, so you don't need to count. The lucky thing is that you don't really need to learn any facts past 9 + 9 (though learning facts through 12 is useful), because you add bigger numbers one digit at a time. Wouldn't it be awful if you had to calculate 1485 + 9385 by counting on your fingers? Even centipedes would have trouble. One thing that I think might help you both with learning the facts and with working out the facts you haven't learned yet, is to find ways to avoid having to count too far. For example, suppose I don't know 8 + 9 yet. The hard way would be to count nine past 8: 8; 9, 10, 11, 12, 13, 14, 15, 16, 17 1 2 3 4 5 6 7 8 9 An easier way is to switch the numbers so you start with the bigger number, 9, and add 8 to it: 9; 10, 11, 12, 13, 14, 15, 16, 17 1 2 3 4 5 6 7 8 An even easier way is to notice that 9 is very close to 10, so you can add 10 (that's easy, right? 8 + 10 = 18) and count backwards: 18; 17 1 This means 8 + 9 is one less than 8 + 10. You can do the same sort of thing with any other facts that you know. If you know 5 + 5 but not 5 + 7, then you can just notice that 7 is 2 more than 5, so 5 + 7 is 2 more than 5 + 5. Another trick that helps a lot is to know all the combinations that add to 10. If you don't know those, work on them first, because they are the most useful facts to know. Here's another way to do 8 + 9. Since I know that 8 + 2 = 10, and 9 is 7 more than 2, then 8 + 9 = 8 + 2 + 7 = 10 + 7 = 17. -------8------- --------9-------- O O O O O O O O X X X X X X X X X -2- ------7------ -------8------- -2- ---------10-------- ------7------ Once you've used these tricks for a while, you should have enough experience to have learned most of the facts, since you learn them best just by using them. Most of us seem to have a few facts that we never quite learn, so these tricks are still useful even when you're grown. And the nice thing about tricks like these is that they help you get to know the numbers better - when numbers are close friends whose habits and personality you know well, math becomes fun. - Doctor Peterson, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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