Number Play — Important Questions

Sum of two odd numbers is even, Sum of an odd and even number is odd, Product of two odd numbers is odd

Odd + Odd = Even (pairs form), Even + Even = Even, Odd + Even = Odd (one leftover), Odd × Odd = Odd, and three odds sum to odd.

15

Sum of 1-9 is 45. In a magic square, each row sum equals 45÷3 = 15.

Only 5

The center appears in 4 lines (2 diagonals, 1 row, 1 column). Only 5 can satisfy all required sums of 15.

Always odd

4n is always even (multiple of 4). Even + 7 (odd) = Odd. So 4n + 7 is always odd.