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Fill in each square in this grid with a digit from 1 to 9. The sum of the digits in each row or column will equal the little number to the left of or above it. See the three-box row at the upper-middle with a 20 to its left? The sum of the digits in those three squares will be 20, and none of the three digits will be the same. A row or column ends at a black square, so the three-square row in the upper-right with a 22 to its left may or may not have digits in common with the 20-row to its left; they’re considered different rows because they’re separated by a black square. Down columns work the same way. Now solve!