classroom.jpgUnit 3 reviews and builds on the telling and solving of story problems. Children will frequently encounter real-life situations that require them to analyze the relationships between known and unknown quantities. Working on story problem strategies helps them apply addition and subtraction skills to the real world. In the previous unit, children solved oral story problems by drawing pictures or circles. In Unit 3, they are introduced to written story problems of various types. They will solve addition problems with an unknown total, addition problems with an unknown partner, and subtraction problems (which also have an unknown partner). To solve these problems, children will learn to count on to find either a total or a partner.

Finding Unknown Numbers
Children are now familiar with the terms partner and total. Unit 3 begins by having students explore situations in which either the total or one of the partners is unknown. The first step in solving one of these problems is recognizing which of these components must be found. In previous units, students learned how to solve problems to find an unknown total, and they used an unknown partner form to subtract. In this unit, children will find an unknown partner in problem situations. Math Expressions clarifies the process by using Math Mountains. In a Math Mountain, the total sits at the top of the mountain and the two partners sit at the base. Children can relate to this representation quickly because they can visualize stones at the top of the mountain rolling down the two sides. If one of the partners is unknown, children count on to find it.

Counting On
In this unit, children are taught to see both subtraction problems and problems with unknown addends as situations with an unknown partner. These two kinds of problems are solved in the same way because they each require an answer to the question, "How many more do I need to reach the total?" In both types of problems, children can count on from the partner to the total to find the unknown partner.

Fuson, Karen, Math Expressions, Unit 3 Overview