Lesson objective: Solve problems by using the most efficient computation strategy.
This lesson provides an opportunity for students to apply their knowledge and understanding of addition and subtraction strategies to a reallife situation. Students are asked to use computational strategies to decide which two carnival attractions to ride based on the number of tickets they have to spend.
Key Concept students will use:

We can use strategies such as making a ten, counting on, and using the relationship between addition and subtraction to add and subtract within 20.
Skills students will use:
 Representing and solving an addition/subtraction word problem within 10 (Unit K10; K.OA.A.2)
 For any number one to nine, there is another number that can be added to it to make 10 (Unit K12; K.OA.A.4)
 Understanding that the meaning of addition and/or subtraction doesn’t change when different strategies are used (Unit K10)
Students engage in Mathematical Practice 3 (Construct viable arguments and critique the reasoning of others) as they explain why a certain computation strategy is efficient for the numbers they are adding and subtracting.
Key vocabulary:
 addition strategies
 counting on
 making a ten
 open number line
 related facts
Special materials needed:
 counters or interlocking cubes
 number line 020