say I have a bunch of numbers (eg I have bought nine boxes of matches and counted how many matches in each box) I found 44, 45, 51, 44, 39, 41, 47, 44 and 45 so there was one box with 39 matches one box with 41 matches three boxes with 44 matches two boxes … Read more

This is ONLY if it is a SQUARE

p=perimeter, n= length of side, a=area

p=4n
a=nxn = n²
a=(p/4)²

so divide by 4 then times that number by itself.