If the perimeter of a rectangle is 18 inches and one side is one inch shorter than the other how long are the sides

Start with appropriate representations: L = length and W = width. Then W = L - 1.

The perimeter is P = 18 in = 2L + 2W, which here would be:

18 in = 2L + 2 (L - 1), or 18 in = 4L - 2. Solving for L:

20 in = 4L, and L = 5 in.

Then W = 5 in - 1 in = 4 in.

Note that 2W + 2L does come to 18 in here: 2 (5 in) + 2 (4in) = 18 in.

The side lengths are 4 and 5 inches, respectively.