 In this series of lessons, students learn to analyze and solve a third basic type of word problem based on a single operation of addition or subtraction. These problems are all based on situations that can be described as “comparison” situations. In this type of problem the situation described is based on two independent groups of things that are independent of each other. There is no set-subset relationship.

In comparison problems, the sum represents the larger of the two groups. The two addends are the smaller group and the difference in the size of the two groups.

Students learn a systematic strategy for identifying the elements described in the problem as the larger group and the smaller group, and the fact that they are independent. They then match the elements in the problem to the two groups and the difference. When the unknown number is the larger group and the smaller group and the difference are given, they learn to add the known values to find the larger group. When the larger group is known and the unknown number is the smaller group or the difference, they learn to subtract to find the unknown group or the difference.

### Word Problems: Add/Subtract – Comparison, Part 1

In the first lesson in this series, students identify the larger of the two groups.

### Word Problems: Add/Subtract – Comparison, Part 2

In this lesson, students identify the larger of the two groups, then write a number sentence in words to describe the relationship between the larger and smaller groups.

### Word Problems: Add/Subtract – Comparison, Part 3

In this lesson, students write a number sentence in words as they did in the lesson before, then they fill in the numbers given in the problem that correspond to the two groups or one of the groups and the difference. The unknown group or the unknown difference is identified with the letter x. They then solve the number sentence to find the solution.

### Word Problems: Add/Subtract – Comparison, Part 4

In this lesson, students solve the same kind of problems as they solved in the lesson before, but they don’t write a number sentence in words or numbers. They solve the problem on paper and enter their final answer on screen.

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