A square is changed into a pentagon by building an equilateral triangle on top of it, as shown. By what percent does the perimeter increase going from the square to the pentagon?
Call the side of the square, s......so....its perimeter = 4s
And the perometer of he pentagon = 5s
So......the percent change is [5 - 4] / 4 * 100% = (1/4) * 100% = 25%