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satellite73

  • 5 years ago

Multiply \[24\times 53\] (or any two 2-digit numbers) using 3 multiplications instead of the usual 4

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  1. anonymous
    • 5 years ago
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    no takers on this one?

  2. saifoo.khan
    • 5 years ago
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    No Takers, Only Under Takers!!

  3. anonymous
    • 5 years ago
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    i think this is a computer algorithm problem. cuts down on multiplications

  4. asnaseer
    • 5 years ago
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    I can do it using only two multiplications: 20 x 53 plus 4 times 53 oh - ok - misunderstood the question...

  5. anonymous
    • 5 years ago
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    yeah that is still 4 right?

  6. anonymous
    • 5 years ago
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    use ethiopian multiplication!

  7. anonymous
    • 5 years ago
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    ok, what might that be?

  8. anonymous
    • 5 years ago
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    rosettacode.org/wiki/Ethiopian_multiplication

  9. anonymous
    • 5 years ago
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    http://rosettacode.org/wiki/Ethiopian_multiplication

  10. anonymous
    • 5 years ago
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    wow! not exactly what i had in mind though...

  11. anonymous
    • 5 years ago
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    method i had was somewhat shorter

  12. asnaseer
    • 5 years ago
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    here is a list of algorithms for doing multiplication: http://en.wikipedia.org/wiki/Multiplication_algorithm

  13. anonymous
    • 5 years ago
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    funny i looked here and didn't see it

  14. asnaseer
    • 5 years ago
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    One of these is particularly interesting: http://en.wikipedia.org/wiki/Karatsuba_algorithm

  15. anonymous
    • 5 years ago
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    hint is \[(a+b)(c+d)=ac+ad+bc+bd\] and you need the numbers \[ac, bd, ad+bc\]

  16. anonymous
    • 5 years ago
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    yeah that is it! for example \[53\times 24\] \[5\times 2=10,3\times 4=12,(5+3)(2+4)=8\times 6=48, 48-10-12=26\] 1 2 26 10 __________-- 1 2 7 2

  17. asnaseer
    • 5 years ago
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    yes - until you brought this up I was wasn't even aware of efficient multiplication methods. thanks for opening the door to new knowledge. :-)

  18. anonymous
    • 5 years ago
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    i never knew the name, and only remember it from a discrete algorithms class. in fact it is all i recall from that class

  19. anonymous
    • 5 years ago
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    karatsuba! i will try to remember that name

  20. asnaseer
    • 5 years ago
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    how can we ever forget a name like that! :-)

  21. anonymous
    • 5 years ago
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    especially with a bookmark!

  22. asnaseer
    • 5 years ago
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    lol!

  23. asnaseer
    • 5 years ago
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    I have just invented a way for me to remember this: rabbits hop around and multiply very fast. so what is their favourite meal? "carrot soup" of course! (hence katatsuba)

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