4x4 Number Grid: Find the Missing Number (中文)

解析

Look at the highlighted 2x2 central block: top-left = 2, top-right = 4, bottom-left = 5, bottom-right = ?. The rule is: bottom-right = top-right + bottom-left - top-left = 4 + 5 - 2 = 7. This diagonal subtraction rule applies consistently across the grid's overlapping quadrants.