This is the Goldilock’s puzzle. It has 3 solutions. The first and easiest solution is found after placing a 1 in the central gray box. Placing a 2 in the box gives a moderately difficult solve. Placing a 3 in the central box gives a difficult solve.
Rules: Ordinary Sudoku Rules apply
NOTE: Because this puzzle has multiple solutions, the answer check function will not work.
Watch a solve from Mark Goodliffe here