arrange the numbers 8 to 16 in the square so that the sum of each row (across, down, diagonally) will always be 36. ply help my daughters.

Answer 1

The basic magic square using 1-9

816
357
492

sums to 15

By raising all the values by 7, you use the numbers 8-16, and each row/column/diagonal is raised by 3*7=21, so they sum to 36

a web search on magic squares will reveal many articles on their construction. Odd-order squares are particularly easy.

Answer 2

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Answer 3

716
359
482
adds to 140