Subtraction word problems
When do we subtract in a word problem? When something is taken away from the original number, or when we work out the difference between two counts.
Pattern 1: taking away
"There were 14 cookies in the jar. 5 children each ate one. How many were left?"
- At first: 14.
- Taken away: 5.
- Action: taking away → subtraction.
Answer: 9 cookies were left in the jar.14 − 5 = 9.
Pattern 2: comparing (difference)
"Janka has \25 and Peter has \18. How much more does Janka have?"
- Janka: 25.
- Peter: 18.
- Action: difference → subtraction (bigger − smaller).
Answer: Janka has \$7 more.25 − 18 = 7.
Pattern 3: a missing part
"There are 26 children in the class altogether. 12 of them are boys. How many girls are there?"
Answer: There are 14 girls in the class.26 − 12 = 14.
Signal words
In subtraction problems you hear:
- "left, remaining"
- "how many more / fewer"
- "difference"
- "taken away, gone, eaten"
Tip: think about the movement
- Are things being added? → +
- Being taken away? → −
- Comparing who has more / fewer? → −
Watch out: order when comparing
For "how many more / fewer", we always do bigger − smaller:
25 − 18 = 7, not 18 − 25.
The other way round we'd get a negative number, which a second-grader has not learnt yet.
Summary
- We subtract when something is taken away or when we want a difference.
- Signal words: left, how many more / fewer, difference.
- Always: bigger − smaller, so the result is positive.
- Answer in a sentence with a unit.