Standard - 2.NBT.5:
Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.

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

Standard - 2.NBT.7:
Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

Standard - 2.NBT.8:
Mentally add 10 or 100 to a given number 100-900, and mentally subtract 10 or 100 from a given number 100-900.

Standard - 2.NBT.9:
Explain why addition and subtraction strategies work, using place value and the properties of operations.