Math

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Solve the mathematical puzzle.

Determine the digits of R from these clues.

The first digit is the answer when the third digit is divided by 2.

The second and third digits add to 7.

The second digit minus the first digit is 1.

R is a three-digit number: ____


I have never understood how to do this.

  • Math -

    Call the digits a,b,c left-to-right

    a = c/2
    b+c = 7
    b-a = 1

    we see that c=2a, so

    b+2a=7
    b-a=1
    subtract to get
    3a=6
    a=2
    Thus c=4 and b=3
    R=234

    Or, just working with the specs,
    c must be even, since it can be divided by 2. So, R is one of the forms
    1x2
    2x4
    3x6
    4x8
    Since the last two add to 7, R must be
    152
    234
    316

    Since 2nd-1st=1,
    R=234

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