Math Games

Grade 2 - Number

Standard 2.N.2 - Practice subtracting half from a number. Recognize the similar numbers in subtracting half of a number.

Included Skills:

Demonstrate understanding of addition (limited to 1 and 2-digit numerals) with answers to 100 and the corresponding subtraction by:
• representing strategies for adding and subtracting concretely, pictorially, and symbolically
• creating and solving problems involving addition and subtraction
• estimating
• using personal strategies for adding and subtracting with and without the support of manipulatives
• analyzing the effect of adding or subtracting zero
• analyzing the effect of the ordering of the quantities (addends, minuends, and subtrahends) in addition and subtraction statements.
• 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).