Primary Standards:

MAFS.1.OA.1.2 Solve word problems that call for addition of three whole numbers whose sum is less than or equal to 20, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

Connecting Standards:

MAFS.1.OA.2.3 Apply properties of operations as strategies to add and subtract.3 Examples: If 8 + 3 = 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 + 10 = 12. (Associative property of addition.)

MAFS.1.OA.3.6 Add and subtract within 20, demonstrating fluency for addition and subtraction within 10.

Content Knowledge:

This Unit will be the first time most students see addition with more than two numbers.  Students should use word problems involving three addends with Add To – Result Unknown and Put Together – Total Unknown problem structures.

Scaffold student instruction to begin with concrete models, pictures, number lines, words, and writing equations.  Students should be given opportunities to explain their thinking by sharing models and strategies to solve the problems.  As they share solutions, the focus should be on strategies that added in different orders but resulted in the same sum.  Strategies may also focus on breaking apart numbers to create “friendly” or “easier” numbers to work with.  These strategies may connect to “making-a-ten” or “using doubles.”  This is the Commutative Property and Associative Property at work, though students do not need to formally know or label the names for these properties.

Work in this Unit will continue to develop both students’ understanding of the operation of addition, as well as build upon fluency and fluency strategies.  The major focus should be around students thinking flexibly and creatively about numbers to come up with meaningful strategies for finding sums of three addends.  This Unit should place emphasis on students comparing/contrasting strategies based on number sense and realize the order of the addends does not change the value.  (i.e. in addition, we can “move the numbers around”)

GCG 1 – Learning Goal: As a Mathematician, I will be able to Add with 3 Addends (within 20)

  • Step 1: Solve Three Addend Problems within 20 using concrete tools, models and drawings
  • Step 2: Solve Three Addend Problems within 20 by re-arranging and grouping addends
  • Step 3: Solve Three Addend Problems using expressions and equations within 20
  • Step 4: Solve for Three Addend Word Problems within 20