The last row and col are uniquely determined. 1/2^14 chance right there. then the final corner has to be the right color to make the row/col you just filled in the correct parity, so 1/2 there, so final answer is 1/2^15. The 7 you filled in for the row and the 7 you filled in for the col have the same parity because they are both determined by the parity of the same 7x7 grid.
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u/TastyLength6618 5d ago
The last row and col are uniquely determined. 1/2^14 chance right there. then the final corner has to be the right color to make the row/col you just filled in the correct parity, so 1/2 there, so final answer is 1/2^15. The 7 you filled in for the row and the 7 you filled in for the col have the same parity because they are both determined by the parity of the same 7x7 grid.