A farmer is building a square pen 21 ft each side. He puts one post on each corner and one post every three in between how many post will he use? Show work and explain what you did

He will use 28 poles.

First, he will need 4 poles for the corner.

Second, each side is 21 feet. If we divide that into 3 foot sections, there will be 7 sections. It will take 6 poles to divide up the sides into 7 sections.

Therefore, he has 6 poles for each side and 4 corners.

6 (4) + 4

24 + 4

28