Lesson 1.1 · Addition and Subtraction Within 20
Counting on to add
You don't have to count every thing from 1 to add. There is a faster way! Start with one number and count on.
Start at the first number
What is ?
You already know there are 8. So don't count them again. Say 8 in your head. Then count on 3 more.
8 … 9, 10, 11
You said 3 numbers after 8. You landed on 11. So .
Count on
To add, say the first number. Then count up one number for each thing you add. The last number you say is the answer.
Start with the bigger number
What is ? You could start at 2 and count on 9. That is a lot of counting!
It is easier to start at the bigger number. Start at 9 and count on 2: 10, 11.
The answer is the same either way. and .
Worked example: Count on with apples
What is ?
🍎🍎🍎🍎🍎🍎🍎 and 🍎🍎
Say 7. Count on 2: 8, 9.
.
Worked example: Start with the bigger number
What is ?
12 is bigger. Say 12. Count on 3: 13, 14, 15.
.
Worked example: Use your fingers
What is ?
Say 14. Put up one finger for each number you count: 15, 16, 17, 18. Stop when 4 fingers are up.
.
Common mistake
Don't count the first number again. For , say "8" and then 9, 10, 11. Don't say "8, 9, 10."
Tip
Use your fingers to keep track of how many you counted on.
Practice
What is ?
Type a number.
What is ?
Type a number.
Mia has 10 stickers. She gets 3 more. How many stickers does she have now?
Type a number.
What is ?
Type a number.
What is ?
Type a number.
What is the easiest way to find ?
What is ?
Type a number.