Mr. Hobbs had an ugly blob in the middle of his wall. The paint on the rest of the wall looked fresh, so Mr. Hobbs asked the painter to come and paint only the blob. The painter said he would charge according to the area that needed to be painted. To figure out how much the job would cost, Mr. Hobbs ran a string around the edge of the blob so that it covered the border perfectly. Then, to figure out the area, he removed the string, shaped it into a rectangle, and figured out the area of the rectangle.
How close did Mr. Hobbs's estimate come to the painter's bill for painting the blob?