Number Grid

Answer

29

Why it works

Every completed row, column, and diagonal adds to 51, so the unfinished middle column fixes the missing number.

1. The top row totals 51: 26 + 5 + 20.
2. The middle row also totals 51: 11 + 17 + 23. The complete columns and diagonals follow that same total.
3. The middle column must therefore total 51: 5 + 17 + ? = 51.
4. Since 5 + 17 = 22, the missing number is 51 − 22 = 29.
5. The bottom row verifies it: 14 + 29 + 8 = 51.