In Kindergarten you learned to count on from any number and small facts. Counting on is a quick way to add.
Key idea
To add, start at the bigger number and count on the smaller number.
Why it works
The bigger number is already counted, so there is no need to count it again. Counting on just the small part is quicker, and the total is the same.
Worked example: Count on 3
What is $8 + 3$?
- Start at 8. Say it, and keep it in your head.
- Count on 3: 9, 10, 11.
- $8 + 3 = 11$
Answer: 11
Worked example: Start with the bigger number
What is $2 + 9$?
- Start at the bigger number, 9.
- Count on 2: 10, 11.
- $2 + 9 = 11$
Answer: 11
Common mistake
Counting the starting number again: “8, 9, 10” gives 10 for $8 + 3$. The first number you say is one more than 8. Hold up 3 fingers, one for each number after 8.
For grown-ups: Have your child say the big number, tap their head (“it’s in here”), then count on with fingers.