LESSON 3
SUBTRACTION
Finding the Difference Between Numbers
What is Subtraction?
Subtraction is the process of taking one number away from another to find the difference. It is the inverse (opposite) of addition and one of the four basic arithmetic operations.
The symbol for subtraction is the minus sign (−). When we write 9 − 4 = 5, we are saying that taking 4 away from 9 leaves us with 5.
Basic Subtraction
Basic subtraction involves taking a smaller number away from a larger one. Think of it as counting backwards. If you have 8 oranges and eat 3, you count back 3 from 8 to get 5.
Subtracting Larger Numbers
When subtracting larger numbers, line them up by place value — ones under ones, tens under tens — and subtract each column from right to left, starting with the ones column.
Borrowing (Regrouping)
When the digit on top is smaller than the digit below it, we borrow from the next column to the left. We take 1 ten and convert it into 10 ones, then subtract.
Checking with Addition
You can always check a subtraction answer by adding the result back to the number you subtracted. If you get the original number, your answer is correct.
Key Facts
The minus sign (−) was first used in print by Johannes Widmann in 1489, the same year as the plus sign.
Subtraction is NOT commutative — 9 − 4 is not the same as 4 − 9.
The answer to a subtraction problem is called the 'difference'. The number being subtracted is called the 'subtrahend'.
Subtraction and addition are inverse operations — each one undoes the other.