Lesson objective: This lesson provides an opportunity for students to apply their knowledge and understanding of addition of three addends in any order to a reallife situation. Students are asked to make a plan and two possible schedules for spending tickets at the carnival.
Key Concept students will use:
 When we are adding numbers together, it doesn't matter what order they are written in.
Skills students will use:
 commutative property of addition.
Students engage in Mathematical Practice 2 (Reason abstractly and quantitatively) as they determine different number combinations that are less than or equal to 20 tickets. Students will also engage in Mathematical Practice 7 (Look for and make use of structure) as they manipulate the number 20 to determine the three missing addends.
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)

addition: a mathematical operation of combining two or more numbers into a total or sum

equal: having the same amount, size, number, or value
 equation: a mathematical sentence stating that two expressions are equal

number line: a line on which a point represents a value or number

order: to place numbers or objects in a sequential arrangement (e.g., least to greatest or heaviest to lightest)

sum: the result when two or more quantities are added

total: the whole amount or value
Special materials needed:
 number lines (020)