Free interactive math game: Rectangle Area — Area = ab. Part of the Geometric Shapes category on MathKite.
Taken from the generator that powers this exercise. A fresh set appears every time the page is opened, and the printable worksheet holds ten of them.
Counting the unit squares that fill a rectangle.
Multiply the length by the width. Picture the rectangle filled with rows of unit squares: the width tells you how many squares sit in a row and the length how many rows there are.
A rectangle 12 cm by 5 cm holds 5 rows of 12 squares, so the area is 60 square centimeters.
Adding the sides instead of multiplying. That gives half the perimeter, which is a length and not an area.