1. Subscribervenda
    Dave
    S.Yorks.England
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    24 Jun '22 08:09
    Correct in every respect Pondy
  2. Subscribervenda
    Dave
    S.Yorks.England
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    27 Jun '22 15:35
    Thankfully, we seem to have gone off the 700 kick:-
    The equation 81-34=47 is true but the reverse equation 74--43 =18 is not true
    Find an example of such an equation using three 2 digit numbers and involving a subtraction which is true in both directions -or prove there isn't one.
  3. SubscriberBigDogg
    Father Mocker
    Wherever
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    28 Jun '22 22:02
    @venda said
    Thankfully, we seem to have gone off the 700 kick:-
    The equation 81-34=47 is true but the reverse equation 74--43 =18 is not true
    Find an example of such an equation using three 2 digit numbers and involving a subtraction which is true in both directions -or prove there isn't one.
    "The equation 81-34=47 is true but the reverse equation 74--43 =18"

    Is that supposed to be only one minus [-] sign in front of the 43?
  4. Subscribervenda
    Dave
    S.Yorks.England
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    29 Jun '22 11:471 edit
    @bigdogg said
    "The equation 81-34=47 is true but the reverse equation 74--43 =18"

    Is that supposed to be only one minus [-] sign in front of the 43?
    Yes
    The equation must be in the format x-y =z
  5. SubscriberPonderable
    chemist
    Linkenheim
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    613051
    29 Jun '22 15:06
    @venda said
    Thankfully, we seem to have gone off the 700 kick:-
    The equation 81-34=47 is true but the reverse equation 74--43 =18 is not true
    Find an example of such an equation using three 2 digit numbers and involving a subtraction which is true in both directions -or prove there isn't one.
    There is no pair that it works for. I can't stringently prove it beyond showing that it won't work for any combination of the second digits...
  6. SubscriberBigDogg
    Father Mocker
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    30 Jun '22 00:28
    I'm not skilled enough at math to prove that there is no solution.

    So I wrote a program and brute forced it. There is no solution.

    Just for giggles, I allowed '0' to be one of the digits. The only solutions found all have at least one '0' in them. This is invalid for the problem, because a 2-digit number ending in 0 will not remain that way once reversed.

    But it does give me some confidence that the program is correct.
  7. Subscribervenda
    Dave
    S.Yorks.England
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    30 Jun '22 13:23
    @bigdogg said
    I'm not skilled enough at math to prove that there is no solution.

    So I wrote a program and brute forced it. There is no solution.

    Just for giggles, I allowed '0' to be one of the digits. The only solutions found all have at least one '0' in them. This is invalid for the problem, because a 2-digit number ending in 0 will not remain that way once reversed.

    But it does give me some confidence that the program is correct.
    You are correct my friend.I'll type out the proof(answer) as given in the paper.
    Hope you enjoyed the challenge.I wouldn't know where to start!
    Reveal Hidden Content
    There isn't one.The equations can be written as 10a+b-10c-d=10e+f and 10f+e=10d+c-10b-a where the letters represent single digits.Subtracting the second equation from the first gives11(a+b-c-d)=9(e-f).This requires e-f to be divisible by 11which is impossible unless e=f then either a and b are both bigger than c and d or one of b or d is 0
  8. Joined
    18 Jan '07
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    10608
    30 Jun '22 18:36
    @venda said
    You are correct my friend.I'll type out the proof(answer) as given in the paper.
    Hope you enjoyed the challenge.I wouldn't know where to start!
    Hidden content removed
    Ooh, I was so close and so far... I had it down to a multiple of 9 also being a multiple of 11, and never considered that, with these being digits, it would imply a number less than 10 being divisible by 11... Shame on me, really.
  9. SubscriberPonderable
    chemist
    Linkenheim
    Joined
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    613051
    01 Jul '22 07:21
    @venda said
    You are correct my friend.I'll type out the proof(answer) as given in the paper.
    Hope you enjoyed the challenge.I wouldn't know where to start!
    Hidden content removed
    ha I had played around with a similar equation an d didn't see the

    Reveal Hidden Content
    divisible by 11 part
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