2025 AMC 10B Problem 23
Problem 23 of 25HarderNumber Theory
A rectangular grid of squares has rows and columns. Each square has room for two numbers. Horace and Vera each fill in the grid by putting the numbers from through into the squares. Horace fills the grid horizontally: he puts through in order from left to right into row puts through into row in order from left to right, and continues similarly through row Vera fills the grid vertically: she puts through in order from top to bottom into column then through into column in order from top to bottom, and continues similarly through column How many squares get two copies of the same number?
Answer choices
Show solution
Solution
At row column Horace writes and Vera writes Set them equal and simplify to get so an integer exactly when For that’s values, and runs all within range. So squares match. Thus, C is the correct answer.