In this lesson, students learn to find the missing addend in an addition sentence. They find the missing addend by using counting on. They start counting on with the next number after the number given. They keep track of how many times they have counted, and stop counting when they reach the sum, which is given. They keep track of the number of times they counted on by clicking to add blocks above the missing addend.
They write the missing added, which is the number of times they counted on.
Subtraction is defined as another way to write addition when one of the numbers that are added is unknown. The minus sign is introduced and defined. They are taught to read a subtraction sentence as 5 minus 3, for example, not 5 take away 3. No reference to “take away” is used in the lesson, or in later lessons when referring to subtraction. This is critical as students will avoid the misunderstanding that subtraction only applies to application situations in which a take away action occurs.
The relationship between subtraction and addition is illustrated by showing how a subtraction sentence can be rewritten as an addition sentence with a missing addend. In the problems in this lesson, students are given a pair of number sentences with the same two numbers, with the third number missing. One is a subtraction sentence and one is an addition sentence. The student enters the missing difference in the subtraction sentence and the missing addend in the addition sentence.
In this lesson, students use what they have learned about subtraction in the lesson before to solve subtraction problems with single digit numbers.