Alex Chui Sets New IMO Record and Poses a 3×3 Grid Puzzle

Last month, Alex Chui, a Year 13 pupil at Tonbridge School in Kent, became the most successful contestant in the history of the International Mathematical Olympiad (IMO). He scored a perfect 42 out of 42, earning a gold medal in Shanghai and bringing his total to seven IMO medals—five of them gold. No participant since the competition began in 1959 has won a medal in seven consecutive years. Chui will begin studying mathematics at the University of Cambridge next term.

The Guardian

Earlier today the Guardian published a puzzle suggested by Chui: fill a 3 × 3 grid with positive whole numbers so that the product of the three numbers in every row and every column equals 30. The numbers in a row or column need not be distinct.

The Guardian

Because 30 = 2 × 3 × 5, each row and each column must contain one factor 2, one factor 3, and one factor 5. The placement of the three 2’s can be chosen in 3 × 2 × 1 = 6 ways (choose a column for the 2 in the first row, a different column for the 2 in the second row, and the remaining column for the third). The same count applies to the 3’s and the 5’s, and the three sets of placements are independent. Multiplying the possibilities gives 6 × 6 × 6 = 216 distinct grids. If multiple primes occupy the same cell, they are multiplied together; empty cells are filled with 1.

The Guardian

The puzzle illustrates Chui’s preference for “clean separation into different parts,” a hallmark of his mathematical style. Publishing the challenge alongside his historic IMO performance highlights both his competitive success and his enthusiasm for sharing problem-solving techniques with a broader audience. Readers were invited to work out the solution before the answer—216 ways—was revealed later in the day.

The Guardian