Illustrative MathematicsVaries

The purpose of this task is for students to solve word problems that call for addition of three whole numbers, to relate counting on to addition, and to understand that the two digits of a two-digit number represent amounts of tens and ones. This task supports developing conceptions of counting on and base-ten structure, and is thus appropriate early in the school year. There is the possibility that students may write different, but correct, equations. If this happens, then the teacher should take the opportunity to ask students whether the different equations are correct and how they know.