In this series of lessons, students learn to analyze and solve one 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 “combination” situations. In this type of problem the situation described is based on two independent groups of things that make up a third, larger group. In other words, they represent a part-part-whole situation. Students learn a systematic strategy for identifying the elements described in the problem as parts of a whole. They then match the elements in the problem to the addends and sum of an addition number sentence. When the unknown number is the sum, they learn to add the known addends. When the unknown number is one of the addends, they learn to subtract to find the unknown addend.

This lesson is preparation for lessons on solving addition and subtraction word problems based on combination situations. Three groups are described in words. The student must identify which of the groups are parts of the third group.

In this lesson, students extend their ability to identify which groups are parts of a larger group by identifying such groups described in a word problem rather than as a set of three named groups as in the lesson before.

In this lesson, students learn to use what they have learned previously about the relationship among groups to write an addition number sentence in words. They are given a word problem and must write an addition sentence that represents the relationship between the groups described in the problem. They do this using a systematic strategy based on first identifying the group that represents the group that contains both of the other groups and labelling that group “all”. They then identify the two groups that make up that group and complete an addition number sentence with the names of these groups.

In this lesson, students extend what they learned in the lesson before. They first read a word problem and write an addition number sentence in words as the did in the prior lesson. Then they enter the numbers given in the problem that correspond to each of the groups for which the value is known. Finally, they enter a “x” for the group for which a value was not given in the problem, which becomes the unknown in the addition statement.

In this lesson, students use what they learned in prior lessons in this series to learn the next step in the systematic solution strategy for problems of this type. They read a word problem, write an addition number sentence in words, fill in the known values for the appropriate groups and x for the unknown group. Finally, they solve the addition sentence to find the value of x, the unknown. If the unknown is the sum, they use addition. If the unknown is an addend, they use subtraction.

At this point, the student has learned all the steps in the strategy used to solve problems of this type. In this lesson they solve the same types of problems, but they are not required to write the appropriate number sentence in words or numbers. They solve the problem on paper and enter their final answer on screen.

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