Question 2
Find the missing number.
a) Four 2 × 2 grids, rows top to bottom: [3, 9; 11, 6], [7, 21; 14, 9], [5, 15; 16, 11], [4, A; 20, C].
b) Three central squares with surrounding numbers (top, left, right, bottom; centre): (12, 18, 3, 12; 45), (19, ?, 13, 12; 55), (4, 8, 9, 3; 24).
**Editorial input note:** Enter A, C, and the missing number in (b), in that order, separated by semicolons with no spaces.
a) Four 2 × 2 grids, rows top to bottom: [3, 9; 11, 6], [7, 21; 14, 9], [5, 15; 16, 11], [4, A; 20, C].
b) Three central squares with surrounding numbers (top, left, right, bottom; centre): (12, 18, 3, 12; 45), (19, ?, 13, 12; 55), (4, 8, 9, 3; 24).
**Editorial input note:** Enter A, C, and the missing number in (b), in that order, separated by semicolons with no spaces.