The number line is an excellent way to model the Part–Part-Whole relationship. Students model problem situations on the number line, and count on or back to illustrate addition or subtraction. The reversibility of addition and subtraction is stressed; a missing addend problem can be solved either with subtraction, or by counting on from the known addend. The difference (the unknown) then becomes an addend to be identified by counting on.
The focus is on identifying the role of the 2 known numbers, and of the unknown number, in the equation. Does the problem include both addends? One addend and the total? Which operation can be used to solve?
All solutions are modeled on the number line. Students write the appropriate equation and draw the solution.
The range of numbers is within 100 and includes problems requiring students to regroup, and some problems with three addends.
A page of blank problems is included. This can be copied and the teacher or students can then write or verbally give problems for additional practice.
Common Core Standards:
2.MD.5: “Use addition and subtraction within 100 to solve word problems involving lengths that are given in the same units...”
2.OA.1: “Use addition and subtraction within 100 to solve one- and two-step word problems involving situations of addint to, taking from, putting together, taking apart, and comparing...”
Subject: Math, Basic operations, Multiplication
Level: Grades 2 – 3
Length/Duration: 12 pages of student work, 2-3 days
Detailed teaching notes and a Smart Notebook 10 file are also included.