Lesson objective: Apply knowledge of the commutative and associative properties to find the sum of three addends in different ways.
This lesson provides an opportunity for students to apply their knowledge and understanding of grouping addends by known facts to a realworld situation. Students are asked to help Mr. Nelson's Class decide what to do for their class party by choosing an item off each list while spending all 16 marbles.
Key Concept students will use:
 When we are adding numbers together, it doesn't matter how they are grouped.
Skills students will use:
 Commutative Property of Addition
 Associative Property of Addition
Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they analyze word problems for important information to help them understand and find a solution. Students also engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they look for facts they already know to help them add three numbers more efficiently.
Key vocabulary:

addend: one of the numbers in an indicated sum of two or more numbers (e.g., 4 + 3 + 1 = 8; 4, 3, and 1 are addends)
 double fact: an addition equation in which each addend is the same

equation: a mathematical sentence stating that two expressions are equal
 group: a number of people or objects that are assembled together or that have some unifying relationship
 known fact: an equation that can be automatically and correctly stated without counting
 sum: the result when two or more quantities are added

ten fact: an addition equation with two addends that total or equal ten
Special materials needed:
 double ten frames
 multicolored counters