number and operations in Base ten 2.nBt
Use place value understanding and properties of operations to add
Fluently add andsubtractwithin 100 using strategies based on place value, propertiesof operations, and/or the
relationship between addition and subtraction.
Add up to four two-digit numbers using strategies based on place value and properties of operations.
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 thestrategy 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 tensor
Mentally add10 or 100 to a given number 100–900, and mentally subtract 10 or 100 from a given number100–900.
Explain why addition and subtraction strategies work, using place value and the properties of operations.