A puzzle is 5 puzzle pieces high and 5 puzzle pieces wide. If you only laid the edges of the puzzle, how many puzzle pieces did you use?

the edges only would be 16 pieces.

Step-by-step explanation:

Think of it as a square. The top row is 5 pieces, bottom row is 5 pieces.

The left vertical side is 3 and the right vertical side is 3. Because the corner pieces are already there, you don't count them twice.