Fluent addition and subtraction
Recall and use addition and subtraction facts to 20 fluently, and derive and use related facts up to 100
What a learner can do afterwards
- Rapidly recall 7 + 8 = 15 and 15 − 8 = 7
- Use 6 + 4 = 10 to derive 60 + 40 = 100
- Derive 35 + 5 = 40 from knowledge that 5 + 5 = 10
1 · Read
Practise facts to 20 so you can remember them more quickly. Use a drawing or a known fact when you need help. To make ten, split one number, keeping all its parts. Fill ten first, then add the rest. A double adds two equal groups. A near double adds one more than a double.
Addition joins two parts into a total. Subtraction can take either part from that total. If 8 + 5 = 13, then 13 − 5 = 8 and 13 − 8 = 5. Start subtraction with the total. Taking one part away leaves the other. Add the parts again to check.
A ten is a group of ten ones. A two-digit number has tens on the left and ones on the right. Since 2 + 8 = 10, 2 tens plus 8 tens make 10 tens: 20 + 80 = 100. Change both parts to tens when using this fact. In 20 + 8, 2 tens and 8 ones make 28.
Use subtraction facts with tens too. Since 9 − 3 = 6, 9 tens take away 3 tens leave 6 tens: 90 − 30 = 60. For a missing part in 30 + [ ] = 90, find 9 − 3 = 6. The missing part is 6 tens, or 60.
For 37 + 3, split 37 into 30 and 7. Since 7 + 3 = 10, the ones make one new ten. Keep the 30 and join it to that ten: 30 + 10 = 40. For 37 + [ ] = 40, the same fact tells you to add 3.
When counting back, count moves, not the starting number. For 12 − 4, move to 11, 10, 9, then 8. Check with 8 + 4 = 12. Reaching 7 would take five moves. You can check addition with subtraction too: 8 + 4 = 12 matches 12 − 4 = 8.
Practise facts to 20. Use known facts to check answers, work with tens and reach the next ten.
Lesson, questions and flashcards written for this learning dataset.
Readings and extra questions written for this learning dataset. Videos by Khan Academy: Adding by making a group of 10 and Adding 53+17 by making a group of 10.
More to read
A double can help
If you know 6 + 6 = 12, you can use it for 6 + 7. The second group has one more, so the total is one more than 12: 13. Draw the groups to check. Practise the fact again later. A known fact or a drawing can help while you learn to remember.
Count the tens
Three tens and five tens make eight tens. You can use 3 + 5 = 8 to write 30 + 50 = 80. Subtraction works with tens too. Since 8 − 5 = 3, taking five tens from eight tens leaves three tens: 80 − 50 = 30. Say tens as you work so you keep track of the groups.
Keep the tens you have
To work out 26 + 4, split 26 into 20 and 6. Six and four make ten. Keep the 20 and add the new ten: 20 + 10 = 30. The same fact helps with 26 + [ ] = 30. Six needs four to make ten, so the box holds 4.
Check with the other operation
Five and nine make fourteen: 5 + 9 = 14. Start with that total to subtract. Taking away 5 leaves 9, and taking away 9 leaves 5. These facts can check each other. For 14 − 9 = 5, add the parts back: 5 + 9 = 14.
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2 · Watch
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