Addition & subtraction word problems
Theory
To solve a word problem, decide whether to add or subtract, set out the calculation, and answer the question asked. A bar model of two parts and a whole shows which operation to use.
A word problem describes a situation in words; your job is to turn it into a calculation.
Add to put amounts together (altogether, total, combined). Subtract to take away or compare (left, how many more, difference).
A bar model shows two parts making a whole. If the whole is missing you add; if a part is missing you subtract.
Words in the question hint at the operation, and a bar model confirms it:
| Missing | Operation | Word clues |
|---|---|---|
| The whole | add | altogether, total, combined, in all |
| A part | subtract | left, how many more, difference, change |
How to solve a word problem
- Read the whole problem and picture it as parts and a whole.
- Decide: whole missing means add; a part missing means subtract.
- Calculate, then answer in words with the amount and what it counts.
The whole is missing, so add.
| \(348 + 276\) | \(=\) | \(624\) |
There are \(624\) students.
A part is missing, so subtract.
| \(1250 - 875\) | \(=\) | \(375\) |
There are \(375\) L left.
“How many more” compares, so subtract.
| \(615 - 480\) | \(=\) | \(135\) |
Team A scored \(135\) more.
| \(4500 + 2750\) | \(=\) | \(7250\) |
The club raised $7250.
Common pitfalls
Frequently asked questions
How do you know whether to add or subtract?
Picture the problem as two parts and a whole. If the whole is missing, add; if a part is missing, subtract.
What is a bar model?
A bar model draws the amounts as a bar split into parts. It shows what is known and what is missing, which tells you the operation.
Which words usually mean subtract?
Left, how many more, difference and change usually mean subtract, because they take away or compare.
How should you answer a word problem?
With the amount and what it counts, such as “624 students”, not just a bare number.