Generalize rules for adding when one addend is zero and for subtracting zero from a quantity and use concrete, pictorial, physical, or oral models to explain the reasoning.

Verify rules generalized for addition and subtraction involving a quantity of zero.

Model concretely, pictorially, or physically situations that involve the addition or subtraction of 1 and 2-digit numbers (with answers to 100) and explain how to record the process shown in the model symbolically.

Generalize and apply strategies for adding and subtracting 1 and 2-digit numbers (with answers to 100).

Create, model symbolically (and concretely, pictorially, or physically if desired), and solve addition and subtraction problems related to situations relevant to one's self, family, or community.

Critique the statement "You can add or subtract numbers in any order and still get the same answer" and provide examples to support the critique.

Select and explain a mental mathematics strategy that can be used to determine a sum of up to 18 (or related difference):

• doubles (e.g., for 4 + 6, think 5 + 5)
• doubles plus one (e.g., for 4 + 5, think 4 + 4 + 1)
• doubles take away one (e.g., for 4 + 5, think 5 + 5 – 1)
• doubles plus two (e.g., for 4 + 6, think 4 + 4 + 2)
• doubles take away two (e.g., for 4 + 6, think 6 + 6 – 2)
• making 10 (e.g., for 7 + 5, think 7 + 3 + 2)
• building on a known double (e.g., 6 + 6 = 12, so 6 + 7 = 12 + 1 = 13)