Okey, now it’s time to learn the Trachtenberg system. It is a system very close to
vedic mathematics I explained before.
Let’s begin by looking at multiplications. When you multiply two different numbers you always have to place as many numbers of zeros in front of the multiplicant as there a digits in the multiplier. So, if you should multiply 123 with 34 you have to look at 123 as 00123. 1234 * 4 then it’s 01234. Ok?
Each number has a “neighbour” to the right, except the last digit. 1234, where 2 is the neighbour to 1, 3 is the neighbour to 2, 4 is the neigbour to 3 and no one is the neighbour to 4.
Ok, we begin with multiplication by 12. Double each digit, starting from the right, and add the neighbour.
379 * 12 = ?
00379 * 12
9 has no neighbour. 9*2 = 18
(7*2) + 9 = 14 + 9 = 23 (and then the 1 from 18) = 24
(3*2) + 7 = 6 + 7 = 13 (and then the 2 from 24) = 15
(0*2) + 3 = 3 (and then the 1 from 15) = 4
(0*0) + 0 = 0
379 * 12 = 4 548
Multiplication by 11.
First recopy the last digit, then add the number with the one before on the rest.
4 862 * 11 = ?
004862 * 11
2 = 2
6 + 2 = 8
8 + 6 = 14
8 + 4 = 12 (and add the 1 from 14) = 13
4 + 0 = 4 (and then add the 1 from 13) = 5
0 + 0 = 0
4 862 * 11 = 53 482
Multiplication by 3.
Rules:
1. Take ten minus the first number and double this. Add on 5 if the number is odd.
2. Take each successive number from 9 and double this. Add half the neighbour. Add on 5 if the number is odd. (rule: “half”)
3. Write down a zero next to the last number. Subtract two from half its neighbour. (rule: “half”)
4 932 * 3 = ?
04932 * 3
(10 - 2) * 2 = 16
((9 - 3) * 2) + (2/2) + 5 = 12 + 1 + 5 = 18 (add the 1 from 16) = 19
((9 - 9) * 2) + (3/2) + 5 = 0 + 1 + 5 = 6 (add the 1 from 19) = 7
((9 - 4) * 2) + (9/2) = 10 + 4 = 14
(4/2) - 2 = 0 (add the 1 from 14) = 1
4 932 * 3 = 14 796
Multiplication by 4.
Rules:
1. Take ten minus the first number. Add on 5 if the number is odd.
2. Take each successive number from 9 and add half the neighbour. Add on 5 if the number is odd. (rule: “half”)
3. Write down a zero next to the last number. Subtract one from half its neighbour.
4 932 * 4 = ?
04932 * 4
10 - 2 = 8
(9 - 3) + (2/2) + 5 = 6 + 1 + 5 = 12
(9 - 9) + (3/2) + 5 = 0 + 1 + 5 = 6 (add the 1 from 12) = 7
(9 - 4) + (9/2) = 5 + 4 = 9
4 - 3 = 1
4 932 * 4 = 19 728
Multiplication by 5.
Rules:
1. Take half of each numbers neighbour. (rule: “half”)
2. Add on another 5 if the number is odd.
3. Write down a zero to the last (left) number.
4 932 * 5 = ?
04932 * 5
0/2 = 0 (has no neighbour)
(2/2) + 5 = 6
(3/2) + 5 = 6
9/2 = 4
4/2 = 2
0/2 = 0
4 932 * 5 = 24 660
Multiplication by 6.
In this case you have to think about a rule called “half”. Half is the number divided by another minus the rest. For example 7/2 = 3 and not 3,5.
This is what you do:
1. Add half the neighbour to each number.
2. Add on another 5 if the number is odd.
3. Write down a zero next to the last (left) number and repeat the above.
4 932 * 6 = ?
04932 * 6
2 (has no neighbour)
3 + 1 + 5 = 9
9 + 1 + 5 = 15
4 + 4 = 8 (and add the 1 from 15) = 9
0 + 2 = 2
4 932 * 6 = 29 592
Multiplication by 7.
3 steps:
1. Double each number and add half its neighbour. (rule: “half”)
2. Add on another 5 if the number is odd.
3. Write down a zero next to the last (left) number.
4 932 * 7 = ?
04932 * 7
2 * 2 = 4 (has no neighbour)
(3 * 2) + 1 + 5 = 12
(9 * 2) + 1 + 5 = 24 (add the first 1 from 12) = 25
(4 * 2) + 4 = 12 (add the first 2 from 25) = 14
(0 * 2) + 2 = 2 (add the first 1 from 14) = 3
4 932 * 7 = 34 524
Multiplication by 8.
Rules:
1. Take ten minus the first number and double this.
2. Take each successive number from 9 and double this. Then add its neighbour.
3. Write down a zero next to the last number and subtract two from its neighbour.
4 932 * 8 = ?
04932 * 8
(10 - 2) * 2 = 16
((9 - 3) * 2) + 2 = 12 + 2 = 14 (add the 1 from 16) = 15
((9 - 9) * 2) + 3 = 0 + 3 = 3 (add the 1 from 15) = 4
((9 - 4) * 2) + 9 = 10 + 9 = 19
4 - 2 = 2 (add the 1 from 19) = 3
4 932 * 8 = 39 456
Multiplication by 9.
Rules:
1. Write down ten minus the first number.
2. Take each successive number from 9 and add its neighbour.
3. Write down a zero next to the last number and subtract one from its neighbour.
4 932 * 9 = ?
04932 * 9
10 - 2 = 8
(9 - 3) + 2 = 8
(9 - 9) + 3 = 3
(9 - 4) + 9 = 14
4 - 1 = 3 (and add 1 from 14) = 4
4 932 * 9 = 44 388
Multiplication by 10, 2, 1 and 0.
Well, I’m not sure if I have to go thru this one but here it is.
To multiply by two, double each number.
To multiply by ten, write down a zero at the end of the number.
Any number multiplied by 1 is itself and multiplied by zero is zero.
So, that was it for now. I hope you have learned something and start to use your head more when calculating.
Related links:
Practice Trachtenberg multiplications
Trachtenberg system on Wikipedia