Adding and subtracting
The biggest pile of word problems in Grade 3 is "add or subtract within 1000". The plan is simple:
Read → identify the question → decide + or − → compute.
Add — "how many altogether?"
If the problem brings two amounts together, you add.
Anna has 245 stamps. Peter has 178. How many altogether?
- Bring together → add.
- 245 + 178 = 423.
- Answer: 423 stamps.
Words: altogether, total, in all, both.
Subtract — "how many left?"
If something is taken away or you want a difference, you subtract.
There were 320 cookies. The class ate 145. How many are left?
- Take away → subtract.
- 320 − 145 = 175.
- Answer: 175 cookies.
Words: left, take away, less, fewer, difference, gave away.
Comparison — "how many more?"
Anna has 245 stamps. Peter has 178. How many more does Anna have?
- "How many more" → subtract the bigger minus the smaller.
- 245 − 178 = 67.
- Answer: 67 more stamps.
Watch out
Words don't always pick the operation:
Anna gave 50 marbles to Peter. Now she has 120. How many did she have at first?
The word "gave" suggests subtraction — but to find the starting amount you have to add them back: 120 + 50 = 170.
Always think about the situation, not just the keyword.
Try it
Summary
- "Altogether / in all / total" → add.
- "Left / fewer / how many more" → subtract.
- The starting amount is sometimes found by adding back.