We tile the rectangle with unit rectangles and show that the area is the same as would be found by multiplying the side lengths. This is the currently selected item. Formula for area of a circle is p Pi times the Radius squared.
Since the classroom is 20 feet long and ten feet wide multiply 20 feet by ten feet to get the area of 200 square feet 20 x 10 200.
The text book lesson for finding area had rectangles with side lengths that were less than one. The area of the outside surface of a solid or three-dimensional shape is called Surface Area. Math 5th grade Multiply fractions Area of rectangles with fraction side lengths. The Perimeter Area and Volume chapter covers the counting method as well as area formulas and examples.