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  1. #1
    fatabass is offline Senior Member
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    Default How would you solve this? Java coding for multiplication.

    *** ( Some number with 3 digits )
    ** ( Some number with 2 digits )
    x
    -------------
    ****
    ****
    -----------
    *****

    where all the asterisks are prime digits either: 2,3,5 or 7

    Ideas, approaches, or even code mayde?

  2. #2
    JosAH's Avatar
    JosAH is online now Moderator
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    Default Re: How would you solve this? Java coding for multiplication.

    It cannot be solved because the righrmost digit in the fourth row has to be a zero.

    kind regards,

    Jos
    cenosillicaphobia: the fear for an empty beer glass

  3. #3
    fatabass is offline Senior Member
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    Default Re: How would you solve this? Java coding for multiplication.

    What makes you think that?

    I am sure it is a "can be solved" question.

  4. #4
    pbrockway2 is offline Moderator
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    Default Re: How would you solve this? Java coding for multiplication.

    Quote Originally Posted by JosAH View Post
    righrmost
    @OP: Can you post again using code tags, because it makes a difference. Put [code] at the start of the calculation and [/code] at the end. That way the formatting will be preserved and we can all see what is supposed to line up with what.

  5. #5
    fatabass is offline Senior Member
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    Default Re: How would you solve this? Java coding for multiplication.

    How would you solve this? Java coding for multiplication.-puzzle_prime.jpg

  6. #6
    JosAH's Avatar
    JosAH is online now Moderator
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    Default Re: How would you solve this? Java coding for multiplication.

    The last digit of the top two numbers have to be a 3 and a 5 (...3x..5 = ....5 (or ..5x.3 = ....5 is the only possibility), so the last digit of the result is 5 as well. Maybe consistent reasoning like this can help you to solve this puzzle. If there are too many alternatives I'd take the lazy approach (brute force)

    kind regards,

    Jos
    cenosillicaphobia: the fear for an empty beer glass

  7. #7
    fatabass is offline Senior Member
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    Default Re: How would you solve this? Java coding for multiplication.

    I am trying to solve it with Java :)
    Thanks though... :)

    I have this idea of looping for all numbers in the first 2 rows and multiplying them and to check if they are all prime numbers(2,3,5,7)..

    But can there be a better approach ?

  8. #8
    pbrockway2 is offline Moderator
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    Default Re: How would you solve this? Java coding for multiplication.

    Totally slow answer adding nothing removed.

    @OP: That's more or less what I would do.
    Last edited by pbrockway2; 12-23-2011 at 09:17 PM.

  9. #9
    JosAH's Avatar
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    Default Re: How would you solve this? Java coding for multiplication.

    There are four different digits (2, 3, 5 and 7) so you should count in base 4. There are 4x4x4 possible first numbers and 4x4 possible second numbers. You can try them all after mapping 0 --> 2, 1 --> 3, 2 --> 5 and 3 --> 7 and see which numbers have the correct result.

    kind regards,

    Jos
    cenosillicaphobia: the fear for an empty beer glass

  10. #10
    fatabass is offline Senior Member
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    Default Re: How would you solve this? Java coding for multiplication.

    Thank you

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