The key strategy to Region Sum Lines involves lines that are a single cell in one region but three cells in another region. Three and one at the same time. So here’s a puzzle with nine such lines!
Rules:
Normal Sudoku rules apply.
Region Sum Lines: Thick region borders divide each line into segments on which the digits have the same sum. Different lines may have different sums.
Estimated difficulty: 1.5 out of 5
Solve on SudokuPad