Sunday, October 21, 2007

How Do You Multiply?

My husband and I were talking about multiplication the other day and I let slip that I don't have my upper times tables memorized. 5 is about as far as I go.

"So how would you multiply 7*9?"

I answered that I'd do 4*9 and then add it to 3*9. Or I might use the ascending/descending pattern of the 9 times table and count down - 9*9=81, 9*8=72, so 9*7=63 He looked at me like I was crazy.

I probably could memorize the upper tables but I never bothered and this method doesn't seem like much extra trouble to me.

I'm wondering who out there has the tables memorized and who uses tricks or alternate methods?

10 comments:

Deb said...

I do what you do...

7*9 = 7 *10 - 7....

:)

5*8 = 5*6 + 5 +5......

:P

I am actually teaching my kids this way as well....

it works for me.... so i dont; see the harm....

Lorraine M. said...

Memorized, but I'm a math person and ex accounting manager. Hubby doesn't know them, hardly any at all. He doesn't care either. However he has nervous issues about going to a store for an item and not having enough money, can't tell while standing at a cash register if he's been overcharged, doesn't know when I bill doesn't make sense, stuff like that. I don't know if it's because math is just not his thing or because he was so poorly served by schools. So math literacy and logic is something I very much want the kids to have. For that reason I am postponing rote knowledge of facts for as long as possible, but I do want them memorized, after the logic is there.

Dawn said...

DEb - I was looking at JUMP Math (jumpmath.org) and a sample fractions unit they have teaches something similar I think. Just a few of the times tables and then showing how you can double the results and such.

Lorraine - You're weird. I can't relate to you on this matter. :)

Lorraine M. said...

LOL. I can't imagine now knowing times tables. They're as simple to me as the ABCs.

Lisa-Unschooling/Evolved Mom said...

Well. You made me feel better. I can up to my 7 times tables.. then I add.. just like you :-)
My firned once suggested that I may have something called "dyscalculia" a kind of dyslexia of numbers. I am always dropping numbers and transposing them. I CANNOT remeber a number if my life depended on it. Do you have trouble with phone numbers or other numbers you should know??

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Dawn said...

$100 bucks up for grabs? I'm heading over. :)

I don't know if I have similar problems with numbers. I can remember phone numbers but it's gneerally with the use of some kind of trick...if it's 734-2930 (randoly typed) I'd remember the first three by thinking 10+4=14 and the last four by thinking of 29 and 30 in sequence. Sounds complicated now that I'm typing it but I bet you I won't forget that number now. :)

kitten said...

I use the hand method. Lets say you say 9*3 - you hold you hands up and on the left hand put down your 3rd finger (cause you multiply by 3)then you have 2 before the finger you let down and 7 after the finger you put down and the answer is 27.

Rolfe said...

I have to admit that if the answer is much over 50 I probably have to stop and think about it a bit. But thinking is the fun part, right?

Heather said...

I'm lost after 6. I do have 9's, but I've always remembered those in a weird way. It sounds more complicated when I explain it than it works in my head. It goes: 9x7, one less than 7 is 6, 7+3=10, 9x7=63. In school they taught us to add to 9, 6+3 is 9 so 63, but I always did it this way because 10's were easier to add to.

Most of them I know, but have to think about it a sec and say, "Is that right? Crap." I'm drilling, drilling, drilling my kids on multiplication because I don't want them to have the trouble I've had.

Dawn said...

Well, I'm happy to know I'm not the only one out there. Frankly, I don't think it's a failing...It takes a bit of mental gymnastics to multiply our way and as Rolfe pointed out, that's a good thing! :)