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A four digit number, 
n is written as 
WXYZ where 
W,X,Y,Z are all different odd digits. Furthermore 
n is divisible by each of 
W,X,Y,Z. What is the largest possible value for 
W-X+Y-Z ?

A four digit number, n n is written as WXYZ W X Y Z where W,X,Y,Z W, X, Y, Z are all different odd digits. Furthermore n n is divisible by each of W,X,Y,Z W, X, Y, Z . What is the largest possible value for WX+YZ W-X+Y-Z ?

Full solution

Q. A four digit number, n n is written as WXYZ W X Y Z where W,X,Y,Z W, X, Y, Z are all different odd digits. Furthermore n n is divisible by each of W,X,Y,Z W, X, Y, Z . What is the largest possible value for WX+YZ W-X+Y-Z ?
  1. Identify Largest Odd Digit for WW: Identify the largest possible odd digit for WW to maximize the value of WX+YZW-X+Y-Z, considering that WXYZWXYZ must be divisible by WW.\newlineSince WW is the most significant digit of a four-digit number, it cannot be 00, and since it must be odd, the largest possible value for WW is 99.
  2. Determine Largest Odd Digit for \newlineYY: Determine the largest possible odd digit for \newlineYY to maximize the value of \newlineWX+YZW-X+Y-Z, considering that \newlineWXYZWXYZ must be divisible by \newlineYY.\newlineSince \newlineYY must be odd and different from \newlineWW, the largest possible value for \newlineYY that is less than \newlineWW (\newline99) is \newlineYY00.
  3. Identify Smallest Odd Digit for XX: Identify the smallest possible odd digit for XX to maximize the value of WX+YZW-X+Y-Z, considering that WXYZWXYZ must be divisible by XX.\newlineSince XX must be odd and different from WW and YY, the smallest possible value for XX is 11.
  4. Determine Smallest Odd Digit for ZZ: Determine the smallest possible odd digit for ZZ to maximize the value of WX+YZW-X+Y-Z, considering that WXYZWXYZ must be divisible by ZZ.\newlineSince ZZ must be odd and different from WW, XX, and YY, the smallest possible value for ZZ that is not ZZ00 (already taken by XX) is ZZ22.
  5. Check Divisibility of 97139713: Check if the number 97139713 is divisible by each of its digits.\newline97139713 is divisible by 99, 77, 11, and 33.
  6. Calculate WX+YZW-X+Y-Z: Calculate the value of WX+YZW-X+Y-Z with the chosen digits.\newlineW=9W = 9, X=1X = 1, Y=7Y = 7, Z=3Z = 3\newlineWX+YZ=91+73W-X+Y-Z = 9 - 1 + 7 - 3\newlineWX+YZ=8+4W-X+Y-Z = 8 + 4\newlineWX+YZ=12W-X+Y-Z = 12

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