Problem 1

The sum of the nine numbers from 1 to 9 is 45:

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45
So, each row (and column and diagonal) must have a sum of 15. (three rows; 45 ÷ 3 = 15)

Problem 2

The sum of the 16 numbers from 0 to 15 is 120:

0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 = 120

So, each row (and column and diagonal) must have a sum of 30. (four rows; 120 ÷ 4 = 30)



Every row, column, and diagonal has two missing numbers. So far, this highlighted diagonal has the greatest sum. In fact, the two empty spaces in this diagonal must add up to 6 because 15 + 9 = 24 and 24 + 6 = 30. What are the choices?