The four numbers in italics outside the nine circles represent the sum of the numbers in the five surrounding circles. The numbers in the circles can only be 1 to 9 and each number can be used only once. Four numbers have been provided to get you started. Find the number that should be in the center of the X.
Comments on solving the puzzle; a process of eliminating possible values as answers:
Values 6, 7, 8 & 9 are provided and can not be reused.
Starting at Equation (1), unknowns A, B & ? can only be equal to 1, 2, 3, 4 or 5 as shown. All other combinations can not include either a 6, 7, 8 or 9 value.
Equation (2): unknowns B, C & ? can also be equal to 1, 2, 3, 4 or 5 as shown.
Equation (3): unknowns C, D & ? can only be equal to 1, 2 or 3 as shown. Comparing with Equation (2), values 4 & 5 can be eliminated as possible values for C & ?. As a result, unknown B can still be equal to 4 or 5 as shown.
Equation (4): unknowns D, A & ? can be equal to 1, 2 or 4 as shown. Comparing with Equation (3), value 4 can be eliminated as a possible value for D & ?. As a result, the final answer for A can only be equal to 4, ? equal to 1 & D equal to 2 as shown. Comparing with notes (1) & (2), the final answers for B can only be equal to 5 and C equal to 3.
Now insert your final answers into the original puzzle and verify the resulting sums.
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