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    Re: The "golden rule of three" - what's that?
    From: Don Seltzer
    Date: 2018 Feb 11, 23:35 +0000

    'Teacheth, by three numbers given, to find out a fourth, 
    in such proportion to the third as the second is to the first. 

           RULE. - First state the question; that is place the 
           numbers in such order that the first and third be of one 
           kind, and the second the same as the number required;... 
           Multiply the second and third numbers together, and 
           divide product by the first, the quotient will be the 
           answer to the question...' 

    In simple terms, how to solve a ratio problem.

    Today we would most likely express it as a very simple algebraic 
    equation. In earlier times it was taught as part of basic arithmetic 
    as a rote procedure; put the known values in a specific order, 
    mulitply, divide, and you have the answer. 


    Don Seltzer



    On Sun, Feb 11, 2018 at 6:19 PM Tony Oz <NoReply_TonyOz@fer3.com> wrote:

    Hello.

    I'm reading the "History of Nautical Astronomy", Mr Cotter describes the state of (apparently insufficient) mathematical literacy of seamen of 15th century like that:

    ...importance in introducing to the English seamen ... the elements of mathematics beyond the golden rule of three.

    What is that?

    Recently I had some hard time guessing what the "butterfly multiplication method" is. We, in Russia, were never tought anything like that.

    Please comment.

    Regards,

    Tony

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