Multiplication Tables Help?

Question

I have to memorize (or at least know) the multiplication tables from 1-20, meaning 1x1...........1x20.........20x1........20x20

Are there any tricks to getting this accomplished quickly? Thanks

Answer 1

Not really, but really it is not that difficult... one trick is...

any number with a zero at the end, jsut drop the zero and multiply so if you had to multiply 14*20... drop the zero and multiply 14*2, you get 28... then just add the zero back on... so 20*14 is 280... :) prolly wont help too much with the other multiplications but eh... also, remember the rule...

a*b = b*a

so 2*14 = 14 * 2 = 28
15*5 = 5*15 = 75 and so on...

of course 1*any number is that number...

1*3 = 3
1*4 = 4 of course...

and split up number as well...

so 14*13 can also be 14*10 + 14*3

this is called the distributive property of multiplication... because 13 also is equal to 10 + 3 the answer to 14*13 = 14*(10+3) = 14*10 + 3*14... you can even break that up further if you need to...

because 3*14 = 3*(10+4) = 3*10 +3*4

14*13 = 14*10+14*3 = 14*10+3*10+3*4 = 140+30+12=182!

remember anything multiplied by 10 you just add a zero to the end or move the decimal 1 spot to the right...

hope this helped :)

Answer 2

The 1-12 you should know. 15's and 20's you should know. The squares you should know. If you don't, study those first. Beyond that, use your knowledge of algebraic tricks (distributive property, conjugates multiplying to differences of squares) to help.

For examples...
If you know 17² = 289, then
16 × 18 = 288 [17² - 1²],
15 × 19 = 285 [17² - 2²], and so on.

If you know 15² = 225, then
14 × 16 = 224 [15² - 1²],
13 × 17 = 221 [15² - 2²], and so on.

If you know your 20's, then 19's aren't so bad.
14 × 19 = 14 × (20 - 1) = 280 - 14 = 266,
17 × 19 = 17 × (20 - 1) = 340 - 17 = 323, and so on.

Also remember that even numbers are 2 times some smaller number. 18's are double 9's. 16's are double 8's. 14's are double 7's. Regroup and multiply... it's really not too bad.
14 × 18 = (2 × 7) × (2 × 9) = 4 × (7 × 9) = 4 × 63 = 252.

Do 17's with the same distributive property as your 19's.
14 × 17 = 14 × (20 - 3) = 280 - 42 = 238,
18 × 17 = 18 × (20 - 3) = 360 - 54 = 306, and so on.

Good luck! It'll take practice to memorize them, but you can do it... or use these tricks to get the answers in your head relatively quickly.

Answer 3

You can do it in one day, and one day isn't a very long time and you will know it the rest of your life.

Get a bunch of paper and start by writing
1 x 1 = 1
1 x 2 = 2
.
.
1 x 20 = 20
2 x 1 = 2
2 x 2 = 4

When you get to 20 x 20 = 400 do the whole thing over again. Do it a hundred times. Start in the morning and do it all day until you have to go to bed, it won't take you that long though. And you will have it memorized.

Answer 4

I think multiplication by multiple of 5 is easy so we can resolve a wayfor example

7*17 = 7(15+2) = 105 + 14 = 119.

This an be done mentally

Answer 5

Well, where the number nine is concerned, each "product" that has 9 as one of the factors, the sum of the numbers in the product will add up to 9: 09,18,27,36,45,54,63,72,81,90.... but after the number 10 the rule breaks downwith the number 11(99),but then resumes again: 108,117,126,135,144,153,162,171,180 but breaks down again at 21 (189).

Answer 6

here's a trick with your 9's

extend your arms forward and fan out your fingers

put your left pinky down, you'll notice you have 9 fingers left (9x1)

put your pinky up and put down your left ring finger, you'll notice your pinky on the left and 8 fingers on the right (9x2=18... 1 and 8) do the same, one finger at a time, next you'll see 2 and 7 (27) and so on... it works up to 9x10, after that, if you need to know 9x18, add (9x8 + 9x10)= 162 same at 9x18

Answer 7

Write them 10 times each. Then quiz yourself or have someone quiz you.