The case notes
Use a complete unit to find equal sums
This region sum line covers an entire row. Box borders divide it into three parts, and all three parts have the same sum. Watch a worked example, then try the idea in a puzzle.
Put it into practice
Three parts · one sum
This region sum line covers an entire row. Box borders divide it into three parts, and all three parts have the same sum.
Whole row = 45
A full Sudoku row contains one through nine. Its digits add to forty-five, even when we do not know their order.
45 ÷ 3 = 15 each
Those three equal parts use every cell of the row. So forty-five splits three ways: each box segment must add to fifteen.
1 + 5 + 9 = 15
In the first segment, one and five are already given. They make six, leaving nine to reach fifteen.
Complete unit → equal parts
The row gave us the sum. The line carried that sum into each part.
Read the transcript
This region sum line covers an entire row. Box borders divide it into three parts, and all three parts have the same sum. A full Sudoku row contains one through nine. Its digits add to forty-five, even when we do not know their order. Those three equal parts use every cell of the row. So forty-five splits three ways: each box segment must add to fifteen. In the first segment, one and five are already given. They make six, leaving nine to reach fifteen. The row gave us the sum. The line carried that sum into each part.
