Lesson 1

The purpose of this lesson is for students to add or subtract within 1,000 using number relationships.

In a previous unit, students compared three-digit numbers using a number line and considered how close they were to one another and their distance from zero. In this lesson, students compare numbers and use the number line to consider ways to find the difference between 2 three-digit numbers. When locating numbers on the number line, students recognize that when the numbers are relatively close, they can simply count on or count back to determine the difference between the two numbers.

In the second activity, students analyze number lines and counting sequences that increase or decrease by 10 or 100. Using these number relationships, students label number lines by counting on or back by 10 or 100. The work of this activity helps prepare students to use and make sense of computation methods based on counting or adding on by place in upcoming lessons.

In previous lessons, students located and compared numbers on the number line. How did the number line help them make sense of subtraction methods based on counting on by place? How could you use number lines to help students make their thinking visible for others?