Fill the nine numbers 1 ~ 9 in the circle below so that the sum of the numbers in the three circles connected by each horizontal line, vertical line and diagonal line is equal to 15.

Answer:

Add these numbers together,1+9 = 2+8 = 3+7 = 4+6 =10, then we can judge that the common divisor in the middle is 5, so the sum of the numbers of each row, column and diagonal is 15.

2. Properties of Simple and Even Numbers

A pile of sticks, four sticks, and finally one left. Guess whether the number of sticks in this pile is odd or even?

Answer: The total number of sticks in this pile is odd.

Summary 4 is even, so no matter how many times it is taken, it is even. But in the end, I left one, so this pile of sticks is always singular.