10 plus 10 divided and rounded to next 20

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Adj has a total of 1075 dance and rock songs on her system. the dance selection is 4 times the size of the rock selection. write a system of equations to represent the situation.

Points a, b, and c form a triangle. complete the statements to prove that the sum of the interior angles of triangle abc is 180