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.
The sum of numbers with more than one digit can be found by adding each column from right to left, starting with the ones place.
Step 1: Write the second number under the first number so that the ones, tens, and hundreds places are lined up.
Step 2: Add the ones column (3 + 4 = 7). Write the 7 in the ones place of the sum.
Step 3: Add the tens column (5 + 7 = 12). 12 has two digits, but both digits will not fit in the tens place. So, write the 2 in the tens place of the sum, and carry the 1 to the hundreds column. This is called regrouping.
Step 4: Add the hundreds column (1 + 2 + 1 = 4). Write the 4 in the hundreds place of the sum.