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LostInParadise's avatar

Does learning the multiplication table seem less daunting when you realize there are only fifteen entries to memorize?

Asked by LostInParadise (31907points) July 26th, 2019

Here is how to get 15.

The 1 table is transparent.

If you know addition, the 2 table is just adding a number to itself.

For the 5 table, think of dividing by 2 and then multiplying by 10. 5×7 = 7/2×10 = 3.5×10 = 35.

There are two tricks that can be used to multiply by 9. You can multiply by 10 and subtract. 9×7 = 10×7 – 7 = 70 – 7 = 63. Alternatively, use the rule that the first digit is one less than the multiplier and realize the two digits add to 9. So for 9×7, 6 is one less than 7 and 6+3=9.

That leaves 5 numbers – 3, 4, 6, 7 and 8. A 5 by 5 table has 25 entries. 5 of these are along the diagonal – 3×3, 4×4, etc. The remaining ones occur twice – 3×7 and 7×3. It is only necessary to memorize one of these, eliminating (25 – 5)/2 = 10. 25 – 10 =15 entries to memorize. Over the course of a year, that does not seem like all that much.

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9 Answers

JLeslie's avatar

I don’t use the same tricks as you, but I agree each number has its own set of tricks. Times 2 is basically like addition, just doubling.

9’s you only have to visualize half the numbers, because the other half are exactly the reverse. The 9 tables has 18, 81, 27, 72, 36, 63, 45, and 54. The first number is 1 less than what you are multiplying. 9×3, the first number starts with a 2, so 27. Your double check is 2+7=9. In fact, that’s all you really need to remember with 9, the two numbers added equal 9, and starts with 1 less than the number. I never understood why people do that subtraction thing with the 9’s. Subtraction isn’t easy in my opinion, but that’s my opinion, and may be easy for others.

5’s are easy, because we count in 5’s from young ages.

4’s are exactly like 2’s you just double twice. You can do it with 8 also, but depends how big the number is if it gets difficult for someone. Some rhyme like 6×8 is 48, and that covers the 6 and the 8.

You only need to remember half the table, because you can always flip the equation around. If you remember 3×8 you know 8×3.

I don’t remember memorizing times tables. I remember my tricks for each equation.

Edit: I think it’s probably better not to do it as a huge table of numbers and better to just do 2’s one week, then 3’s the next week, etc. That’s how I remember it from my own childhood.

Kardamom's avatar

Math is like reading Russian translated into Klingon for me. And reading tips about how it is so simple always leave me scratching my head, because it still doesn’t make sense to me.

I’ve always felt like I’ve had some kind of missing gene for understanding math.

Dutchess_lll's avatar

Well, it’s like swimming. Just relax and float. It will come. If you fight, which is almost an instinct, you’ll sink.

JLeslie's avatar

@Kardamom So, how did you learn basics in math like 9X4? It’s just rote memorization?

Kardamom's avatar

@Jleslie, yes. And it took me much longer than most other people, and now I have lost almost all of them. Math is extremely difficult for me.

Dutchess_lll's avatar

I still don’t have all the 8s and 9s down and I loved math.

JLeslie's avatar

@Kardamom I guess you have dyscalculia. I was like that with history. Gawd I hated it, and could not remember it, and it made little sense to me. I’m more interested in it now, but still really hard for me to retain. I’m very average at reading comprehension too, especially topics I hate. It’s torture reading things I have no interest in. I guess everyone has something.

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