Ethiopian multiplication: Difference between revisions
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'''Method:'''<br> |
'''Method:'''<br> |
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# Take two numbers to be multiplied and write them down at the top of two columns. |
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# In the left-hand column repeatedly halve the last number, discarding any remainders, and write the result below the last in the same column, until you write a value of 1. |
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# In the right-hand column repeatedly double the last number and write the result below. stop when you add a result in the same row as where the left hand column shows 1. |
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# Examine the table produced and discard any row where the value in the left column is even. |
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# Sum the values in the right-hand column that remain to produce the result of multiplying the original two numbers together |
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'''For example:''' 17 x 34 |
'''For example:''' 17 x 34 |
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17 34 |
17 34 |
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Halving the first column: |
Halving the first column: |
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17 34 |
17 34 |
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8 |
8 |
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2 |
2 |
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1 |
1 |
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Doubling the second column: |
Doubling the second column: |
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17 34 |
17 34 |
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8 68 |
8 68 |
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2 272 |
2 272 |
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1 544 |
1 544 |
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Strike-out rows whose first cell is even: |
Strike-out rows whose first cell is even: |
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17 34 |
17 34 |
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8 -- |
8 -- |
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2 --- |
2 --- |
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1 544 |
1 544 |
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Sum the remaining numbers in the right-hand column: |
Sum the remaining numbers in the right-hand column: |
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17 34 |
17 34 |
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8 -- |
8 -- |
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==== |
==== |
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578 |
578 |
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So 17 multiplied by 34, by the Ethiopian method is 578. |
So 17 multiplied by 34, by the Ethiopian method is 578. |
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The task is to '''define three functions'''/methods/procedures/subroutines: |
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# one to '''halve an integer''', |
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<br>'''The task is to define three functions/methods/procedures/subroutines: to half an integer; to double an integer; and one to state if an integer is even. Use these functions to create a function that does Ethiopian multiplication.'''<br> |
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# one to '''double an integer''', and |
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# one to '''state if an integer is even'''. |
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Use these functions to '''create a function that does Ethiopian multiplication'''. |
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'''References''' |
'''References''' |
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*[http://www.youtube.com/watch?v=Nc4yrFXw20Q A Night Of Numbers - Go Forth And Multiply] (Video) |
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*[http://www.ncetm.org.uk/blogs/3064 Ethiopian multiplication] |
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*[http://www.bbc.co.uk/dna/h2g2/A22808126 Russian Peasant Multiplication] |
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=={{header|C}}== |
=={{header|C}}== |
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