Some expressions contain only addition and subtraction. When this is the case, the rule for evaluating the expression is simple. When an expression contains only addition and subtraction, evaluate it step by step from left to right.
| Expression | Example | Rule |
|---|---|---|
| Contains only addition and subtraction | 12 + 7 – 6 – 3 + 8 | Evaluate left to right. |
| Contains only multiplication and division | 18 ÷ 3 x 7 ÷ 14 | Evaluate left to right. |
| Mixed-operator expression: contains a combination of addition/subtraction and multiplication/division | 9 + 6 ÷ 3 | 1. Evaluate multiplication and division left to right. 2. Evaluate addition and subtraction left to right. |
For example, suppose you want to evaluate this expression:
17 – 5 + 3 – 8
Because the only operations are addition and subtraction, you can evaluate from left to right, starting with 17 – 5:
= 12 + 3 – 8
As you can see, the number 12 replaces 17 – 5. Now the expression has three numbers instead of four. Next, evaluate 12 + 3:
= 15 – 8
This step breaks down the expression to two numbers, which you can evaluate easily:
= 7
So 17 – 5 + 3 – 8 = 7.