Russian Multiplication - a different way to multiply numbers.

Russian Multiplication

This is a short article which describes a different way to multiply two numbers.

All you need to do is divide by two, double a number, and add a column, and know how to recognize even and odd. Using these simple tools, you can multiply any two numbers.

Here is the method by example.

Step 1 Lay out your numbers as the first in two columns. e.g. 35 and 7

35 7

Step 2

Halve the first column and throw away the remainder. Keep doing this until you get to 1.

35 7
17
 8
 4
 2
 1

Step 3

Repeatedly double the other column

35    7
17   14
 8   28
 4   56
 2  112
 1  224

Step 4

Identify all rows where there are odd numbers in the left hand column:

35    7
17   14
 8   28
 4   56
 2  112
 1  224

Step 5

For each of the numbers in the right column where there is an odd number in the left column, add them up.

  7
 14
224
---
245

Now check your answer by casting out nines. (Link)

Or find out how to instantly square a number ending in 5.

Learn about Binary and Hexadecimal too.

 

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Comments 3 comments

Kirui 5 years ago

I like that. I attempted to proof this method. Does it have something to do with expressing number in binary form? I thought those you don't exclude in final addition correspond to zeros in binary form but I didn't work out the details.


insert name here 4 years ago

i dnt get da last sentence bruv! work on ya grammar yeah! simples skillz man, i mean it took me llike 10 mins ta work dat 1 out bruv. i had to getz ma nan and she dint even getcho sentence. so seriously work on it innit.


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Manna in the wild 4 years ago from Australia Author

What an odd comment from the Neville Lovett Community School. Specialist in Mathematics and Computing. English seems to be a problem I see. What are they teaching you in the UK these days?

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