Let's solve the following problem:
Write the missing numbers in the squares so that you get a magic square and find which number should be placed in the place of the question mark.
Magic squares are usually filled so that in every row, column and both diagonals the sum of the numbers is equal.
Step 1
First you have to find the row, column or diagonal sum of three of the filled numbers.
Step 2
Then successively fill in where the third number is missing (by row, column or diagonal) so that the sum is equal.
Answer: 9
* Magic square problems can be found in the course Competitive Mathematics - Level 2