2 1 Addition Combinations Objective I can use

2. 1 Addition Combinations Objective: I can use addition combinations to solve addition problems using mental math

Mental Math n What is it? n Why do we use mental math? n Can you think of examples of when I would use mental math in the real world?

Addition Combinations to Help us with Mental Math Make 10 or 100 Combinations Doubles Near Doubles (+1, -1) Plus 10 or 100 Combinations Plus 9 or 90 Combinations Remaining Combinations

Make 10 or 100 Combinations Numbers that when added together make 10 or 100 Examples: 6 + 4 = 10, 70 + 30 = 100

Doubles Two of the same number added together. Examples : 8 + 8 = 16, 40 + 40 = 80 , 50 + 50 = 100

Near Doubles Numbers that are close to being the same. You add doubles then subtract the difference. Ex. 49 + 50 = (50+50 -1) Ex. 36 + 40 = (40+40 -4)

Plus 10 or 100 Combinations Numbers that are added to 10 or 100. Ex. 49 + 10 = 59, 49 + 100 = 149

Plus 9 or 90 Combinations Numbers that are added to 9 or 90. You should add 10 then subtract 1 or add 100 then subtract 10. Ex. 76 + 9 = (76+10 -1) 76 + 90 = (76+100 -10)

Remaining Combinations All other combinations of numbers. These are harder to do mental math. Ex. 16 + 32 How could I do mental math with this example?

Solve using QUICK mental math. Which mental math combinations did you use? (Ex. 20 + 80) (Ex. 40 + 40) (Ex. 49 + 50) (Ex. 28 + 100) (Ex. 52 + 9)

Left Side Create a 5 tab foldable. n On the outside write the following problems: 1. 89 + 100 2. 60 + 40 3. 71 + 90 4. 45 + 45 5. 33 + 30 n On the inside left of the foldable write the addition combination strategy n On the inside right write the answer (circled) and explain using words how you solve using mental math. n

Left Side Directions: Cut out the addition combinations and glue in your notebook on the left side. For each one solve using mental math. Write down which mental math combination helped you solve, how you solved it in your head, and what you got for your answer. Example: n n n n n 30 + 70 Answer: _________ Combination: _______ Explain how you solved in your head: Make 100 combinations (Ex. 20 + 80) Doubles (Ex. 40 + 40) Near Doubles (Ex. 49 + 50) Plus 100 Combinations (Ex. 28 + 100) Plus 9 Combinations (Ex. 52 + 9)