# 5. 3 Digit - 3 Digit

Subtract a 3 digit number from another 3 digit number without regrouping. In this grade, subtraction by using the standard algorithm should not be the focus. Students should instead practice subtraction based on concepts of place value. For example, to subtract a 3 digit number from another 3 digit number, they can subtract hundreds from hundreds, tens from tens and ones from ones. To understand how this works, they should look at the expanded forms of numbers. For example, 373 - 121 is the same as (300 + 70 + 3) - (100 + 20 + 1). They can now group the hundreds, tens and ones together as (300 - 100) + (70-20) + (3-1) to subtract. It is important for students to know how a particular method works, rather than just using the method. Subtracting by using place concept and value concept will help students make sense of the standard algorithm, when they use it more and more in higher grades.

### Common Core Alignment

**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.