posted by KC .
Helping grandson with math. I would like to know how to do it before he does.
"How many different rectangles can be made with a perimeter of 20 units? (Remember, a square is also a rectangle.)"
I assume you mean with integer lengths
L + w = 10
L = 5, w = 5 as you said
L = 6, w = 4
L = 7, w = 3
L = 8, w = 2
L = 9, w = 1
the ones with w>L do not count because they are indistinguishable from the ones we have now. , So, 5.