Geometric measurement: understand concepts of area and relate to area of multiplication and addition.
Relate area to the operations of multiplication and addition. (3.MD.7)
c. Use tiling to show in a concrete case that the area of a rectangle with whole-number side lengths a and b + c is the sum of a × b and a × c. Use area models to represent the distributive property in mathematical reasoning. (3.MD.7c)
More information and the complete College and Career Readiness Standards can be found here.