use each digit from 1 to 9 to make each line sum to 15. use each digit once

1 + 9 + 5

3 + 8 + 4
2 + 7 + 6

how about arranging the number so that no only do the rows up to 15, but so do all the columns and the two diagonals?

8 1 6
3 5 7
4 9 2

To solve this problem, we need to arrange the digits from 1 to 9 in a way that each line adds up to 15, and each digit is used only once. Let's go step by step:

Step 1: Identify the pairs of numbers whose sum needs to be 15. In this case, we have three pairs: (1, 9), (2, 8), and (3, 7).

Step 2: Place the number 5 in the center, as it will be a part of all three lines.

Step 3: Place the other numbers around the 5, ensuring that each number is used only once. We can start by placing the numbers in the pairs (1, 9) and (2, 8) opposite each other, as shown below:

1 2
9 5 8

Step 4: Fill in the remaining numbers. Since we are left with (3, 7), we can place the 3 below the 2 and the 7 below the 1:

1 2
9 5 8
7 3

Now, let's check if all the lines add up to 15:

1 + 9 = 10
2 + 5 + 8 = 15
7 + 3 = 10

Each line adds up to 15, and each digit from 1 to 9 is used once.

The final arrangement is:

1 2
9 5 8
7 3