2.NBT.6 Add up to four two-digit numbers using strategies based on place value strategies and properties of operations.

Mental Math Warm-Up Add 34 + 51 Be prepared to share your strategy for how you solved it. Teacher Notes: Start by “collecting” answers on your white board, poster paper or easel Once you get a list of answers, ask students which answers can we eliminate? And how do you know they would not work. Ask students to share how they got their answer. Then ask the other students if anyone thought about it the problem in the same way. Ask students to share a different strategy and continue until students have shared their unique ways. Mental Math Warm-Up

Math Strategies 36 + 22+ 12 Which two numbers would you add first? Students could add 22 + 12 to get 34 Then add 34 + 36 in order to make a ten from the ones 10 + 60 = 70 Math Strategies

56 + 12 + 9 Which two numbers would you add first ? Math Strategies

45 + 32 + 23 + 15 Which two numbers would you add first? Students can see how to make tens and fives with these numbers using the associative property 45 + 15 = 60 32 + 23 = 55 60 + 55 = 115 4 two-digit addition

4 two-digit addition Add 37 23 18 14 Students can choose to decompose numbers by tens and ones 30 + 20 + 10 + 10 = 70 7 + 3 + 8 + 4 = 22 With the ones they can use the associative and making a ten 7 + 3 = 10 Split the 4 into 2 and 2 8 + 2 = 10 10 + 10 + 2 = 22 4 two-digit addition

MP 3 Critique the Reasoning of Others My cousin Linda solved an addition problem. Does Linda have the correct answer? 57 + 42 + 24 + 11 = 135 MP 3 Critique the Reasoning of Others