B. Number · Operations: Adding, Subtracting and Equal GroupsAddition Facts to 20
B2.2 B2.1About 30 minutes
Learning goals- I can recall doubles facts up to 10 + 10.
- I can use a double I know to solve a near double.
- I can use make ten to add 9, 8 or 7 to a number.
- I can say many addition facts to 20 quickly, without counting.
Words to know
fact
A small number sentence you can know by heart, like 7 + 8 = 15.
recall
To remember something quickly, without counting.
double
Adding a number to itself, like 6 + 6 = 12.
near double
Two numbers that are one apart, like 6 + 7. Use the double and add 1.
make ten
Break a number apart so one part fills up a ten. 9 + 5 = 9 + 1 + 4 = 10 + 4 = 14.
Let's start with a game
A grown-up says a number from 1 to 10. You shout the double! "Five!" "Ten!" "Eight!" "Sixteen!"
In Grade 1 you learned addition facts up to 10 and some strategies for bigger numbers. In Grade 2, the goal is to know your addition facts up to 20 so well that you can say them fast, like you know your own name.
Why learn facts by heart? Because facts are the building blocks for bigger math. If you know 7 + 8 = 15, you can solve 27 + 8, 70 + 80 and lots more!
You do not have to memorize them one by one. Strategies help you work out a fact fast. With practice, it becomes a fact you just know.
Strategy 1: Doubles
| Double | Sum | Picture it |
|---|
| 1 + 1 | 2 | 2 eyes |
| 2 + 2 | 4 | 4 wheels on a car |
| 3 + 3 | 6 | 6 legs on an ant |
| 4 + 4 | 8 | 8 legs on a spider |
| 5 + 5 | 10 | 10 fingers |
| 6 + 6 | 12 | 12 eggs in a carton |
| 7 + 7 | 14 | 14 days in two weeks |
| 8 + 8 | 16 | 16 crayons in two rows of 8 |
| 9 + 9 | 18 | 18 holes on a golf course |
| 10 + 10 | 20 | 20 fingers and toes |
Strategy 2: Near doubles
When two numbers are next-door neighbours (like 6 and 7), use a double.
6 + 7: I know 6 + 6 = 12. 7 is one more than 6, so 6 + 7 is one more: 13.
You can also use the bigger double: 7 + 7 = 14, and 6 is one less, so 14 − 1 = 13.
Worked exampleExample 1: Near double
- 8 and 9 are neighbours. Use a double.
- 8 + 8 = 16.
- 9 is one more than 8, so add 1 more: 16 + 1 = 17.
Strategy 3: Make ten
Ten is a friendly number. When one number is close to 10, like 9, 8 or 7, fill up a ten first.
9 + 5: 9 needs 1 more to make 10. Take 1 from the 5. Now it is 10 + 4 = 14.
Worked exampleExample 2: Make ten with 8
- 8 needs 2 more to make 10.
- Break 6 into 2 and 4.
- 8 + 2 = 10.
- 10 + 4 = 14.
8 + 6: jump 2 to land on 10, then jump 4 more to land on 14.Worked exampleExample 3: Adding 9 shortcut
- 9 is just 1 less than 10.
- 10 + 7 = 17 is easy.
- But we added 1 too many, so take 1 away: 17 − 1 = 16.
9 + 7 = 16. (Make ten works too: 9 + 1 + 6 = 10 + 6 = 16.)
Strategy 4: Ten plus
Adding to 10 is the easiest of all. 10 + 3 = 13, 10 + 8 = 18. The 1 in the teens means one ten, and the other digit tells the ones.
Which strategy should I use?
- Same numbers? Use a double.
- Numbers next to each other? Use a near double.
- One number is 9, 8 or 7? Make ten.
- Adding 1, 2 or 3? Count on from the bigger number.
- Remember: you can switch the order (3 + 9 = 9 + 3).
| + | 6 | 7 | 8 | 9 |
|---|
| 6 | 12 | 13 | 14 | 15 |
| 7 | 13 | 14 | 15 | 16 |
| 8 | 14 | 15 | 16 | 17 |
| 9 | 15 | 16 | 17 | 18 |
Just for funA spider has 8 legs. Two spiders have 8 + 8 = 16 legs. That's a doubles fact, and a lot of tiny shoes!
Hands-on activityFact flash cards and Snap
You need: 20 small pieces of paper or index cards, and a pencil.
- With a grown-up, write one fact on each card, like 7 + 8, with the answer on the back. Use the tricky facts from the table above.
- Flip through the cards. Say the answer. If you know it in about 3 seconds, put it in the Know it! pile. If not, put it in the Practise pile.
- For the Practise pile, say which strategy helps (double, near double, make ten).
- Play again tomorrow. Try to move cards into the Know it! pile.
Game idea: Lay two cards face up. If they have the same sum (like 9 + 6 and 8 + 7), shout Snap!
Your turn
15. 7 + 7 = 14, and 1 more is 15.
15. 9 + 1 = 10, then 10 + 5 = 15.
13. 8 + 2 = 10, then 10 + 3 = 13.
13. Switch: 9 + 4. Make ten: 9 + 1 = 10, then 10 + 3 = 13.
7Which strategy would you use for 6 + 7? Solve it.
A near double: 6 + 6 = 12, so 6 + 7 = 13.
More practice: on your own
18 + 7 = ? Explain your strategy.
15. Near double: 7 + 7 = 14, plus 1 = 15. (Or make ten: 8 + 2 = 10, then 10 + 5 = 15.)
17. Near double: 8 + 8 = 16, plus 1 = 17. (Or 10 + 8 = 18, then 1 less = 17.)
14. Make ten: 8 + 2 = 10, and 6 − 2 leaves 4. 10 + 4 = 14. (Or double 7 + 7 = 14.)
4Lily has 9 red mitts and 5 blue mitts in the bin. How many mitts?
14 mitts. 9 + 1 = 10, then 10 + 4 = 14.
5Find two different facts that make 16.
Many answers. Examples: 8 + 8, 9 + 7, 10 + 6, 7 + 9, 6 + 10.
Challenge
1Fill in the blank: 7 + 6 = 9 + __
4. 7 + 6 = 13, and 9 + 4 = 13.
2Max says 8 + 9 = 16 because 8 + 8 = 16. What did he forget?
He used the double 8 + 8 = 16 but forgot to add 1 more because 9 is one more than 8. 8 + 9 = 17.
3I am thinking of a double. If you add 1 to it, you get 15. What is the double?
7 + 7 = 14. 14 + 1 = 15. (So 7 + 8 = 15 is the near double.)
Quiz
4. To make ten for 8 + 5, how do you break apart the 5?
5. Which fact has a sum of 17?
Big idea: By the end of Grade 2, the Ontario curriculum (B2.2) expects children to recall and demonstrate addition facts to 20. "Demonstrate" means they can show why a fact is true with counters, ten frames or a number line, not only say it. Strategies (doubles, near doubles, make ten) are the path to recall.
Common mistakes:
- Counting on fingers from 1 every time. Fine at first, but nudge toward strategies: "Can you use a double?"
- Near doubles off by 2 (8 + 9 = 16 or 18). Ask: "Which double did you use? Is the other number one more or one less?"
- Make ten: breaking apart the wrong number. Use two ten frames and real counters so they can see which counters move.
How to help: Practise 5 minutes a day rather than one long session. Card games (Snap, Go Fish for pairs that make a sum), dice games (roll two dice and add) and car rides ("What's 8 + 7?") work well. Keep it light and praise strategies, not just speed.