When you add, does the order matter? Let’s see.
Key idea
You can add two numbers in either order. The sum stays the same: $3 + 8 = 8 + 3$.
Why it works
Adding counts all the things in both groups. Counting the groups in the other order still counts the same things.
Worked example: Same sum
Is $7 + 5$ the same as $5 + 7$?
- $7 + 5$: start at 7, count on 5: 12.
- $5 + 7$: 5 and 5 make 10, and 2 more make 12.
- Both are 12, so yes.
Answer: Yes, both are 12
Worked example: Pick the easy order
Find $2 + 9$.
- $2 + 9$ is the same as $9 + 2$.
- Start at 9 and count on 2: 10, 11.
- $2 + 9 = 11$
Answer: 11
For grown-ups: When your child adds, ask, “Would it be easier the other way around?”