The idea, step by step
Joining makes a new total
When another group joins, keep both groups. Count all the objects or start with the first group and count on.
Use a plus sign to record joining: eight birds and four more birds is 8 + 4.
Taking away leaves fewer
When some objects leave, do not count them in the remaining group. Start with the whole and take away the stated part.
A minus sign records taking away. Fifteen blocks with six removed is 15 − 6. You can move counters away to check.
A common trap
Adding when the story says objects are taken away.
Instead: Act out the story first. If objects leave, the remaining total gets smaller.
See the thinking
More birds arrive
Eight birds are on a fence. Four more land. How many now?
- Keep the eight birds and add the four new birds.
- Count on four: nine, ten, eleven, twelve.
- Record 8 + 4 = 12.
Blocks are put away
There are fifteen blocks. Put six away. How many stay out?
- Start with fifteen.
- Take away six counters, counting them carefully.
- Nine remain: 15 − 6 = 9.
Check your understanding
Six children are playing. Three more join. Which calculation matches?
Show answer
6 + 3 = 9
Both groups stay, so add them.
Your turn
6 questions · Work at your own pace.
Read the questions online
- Five shells and three more shells are joined. How many shells?
- Twelve pencils are out. Four are put away. How many remain?
- Nine children are on a bus. Two get off. How many stay?
- Seven red beads and six blue beads are joined. How many beads?
- There are eighteen counters. Take away eight. Write a calculation and answer.
- Ari has ten cards. Four cards are given to him. Is 10 − 4 a matching calculation? Explain.
Read the worked solutions
- Five shells and three more shells are joined. How many shells?
5 + 3 = 8.
8 shells. - Twelve pencils are out. Four are put away. How many remain?
12 − 4 = 8.
8 pencils. - Nine children are on a bus. Two get off. How many stay?
Taking two away from nine leaves seven.
7 children. - Seven red beads and six blue beads are joined. How many beads?
7 + 6 = 13.
13 beads. - There are eighteen counters. Take away eight. Write a calculation and answer.
Eighteen is ten and eight. Removing eight leaves ten.
18 − 8 = 10. - Ari has ten cards. Four cards are given to him. Is 10 − 4 a matching calculation? Explain.
He receives cards, so the total increases.
No. Use 10 + 4 = 14.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Year 1 additive situations and number bonds within twenty.
Official curriculum source ↗