 How to Evaluate Expressions with Addition and Subtraction - dummies

# How to Evaluate Expressions with Addition and Subtraction

When an expression has only addition and subtraction, in any combination, it’s easy to evaluate: Just start with the first two numbers and continue from left to right. Even when an expression includes negative numbers, the same procedure applies (just make sure you use the correct rule for adding or subtracting negative numbers).

## Sample question

1. Find 7 + –3 – 6 – (–10).

8. Start at the left with the first two numbers, 7 + –3 = 4:

7 + –3– 6 – (–10) = 4 – 6 – (–10)

Continue with the next two numbers, 4 – 6 = –2:

4 – 6– (–10) = –2– (–10)

Finish up with the last two numbers, remembering that subtracting a negative number is the same thing as adding a positive number:

–2 – (–10) = –2 + 10 = 8

## Practice questions

1. What’s 9 – 3 + 8 – 7?

2. Evaluate 11 – 5 – 2 + 6 – 12.

3. Find 17 – 11 – (–4) + –10 – 8.

4. –7 + –3 – (–11) + 8 – 10 + –20 = ?

Following are the answers to the practice questions:

1. 9 – 3 + 8 – 7 = 7.

Add and subtract from left to right:

9 – 3 + 8 – 7

= 6 + 8 – 7

= 14 – 7 = 7

2. 11 – 5 – 2 + 6 – 12 = 2.

11 – 5 – 2 + 6 – 12

= 6 – 2 + 6 – 12

= 4 + 6 – 12

= 10 – 12 = –2

3. 17 – 11 – (–4) + –10 – 8 = 8.

17 – 11 – (–4) + –10 – 8

= 6 – (–4) + –10 – 8

= 10 + –10 – 8

= 0 – 8 = –8

4. –7 + –3 – (–11) + 8 – 10 + –20 = 21.

–7 + –3 – (–11) + 8 – 10 + –20

= –10 – (–11) + 8 – 10 + –20

= 1 + 8 – 10 + –20

= 9 – 10 + –20

= –1 + –20 = –21