Question

18 sections of fence each 1 meter long. What are the various sizes of rectangular pens using all 18 units of fence?

Answer 1

If the dimensions are x and y, and assuming you want integer-length sides, the

2(x+y) = 18
x+y = 9

So, just start listing pairs of positive integers that add up to 9:

1 8
2 7
...