Adding and subtracting · Grade 3
In Grade 3 you learn: adding and subtracting 3-digit numbers; column addition and subtraction; checking with the inverse; two-step word problems.
Adding puts amounts together; subtracting takes away or finds the difference between two amounts. They are opposites: one undoes the other, so every subtraction can be checked with an addition. Good mental strategies (counting on, partitioning, using bonds) make both quick and reliable.
Key facts
- Adding can be done in any order: 7 + 5 = 5 + 7. Subtracting cannot.
- Partition to add: 47 + 35 = 40 + 30 + 7 + 5 = 82.
- Find a difference by counting up from the smaller number.
- Fact family: if 46 + 37 = 83 then 83 − 37 = 46 and 83 − 46 = 37.
- Check a subtraction by adding the answer back on.
- Look for pairs that make 10 or 100 when adding three numbers.
Worked examples
Example 1
8 + 5
Answer: 13