Lesson 8 of 8 · Grade 1
Fact families
Three numbers can make four facts: two adds and two take aways.
Step 1
Learn it
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Three numbers
Take 3, 4 and 7. 7 is the whole. 3 and 4 are the parts.
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Two adds
3 + 4 = 7 and 4 + 3 = 7.
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Two take aways
7 − 3 = 4 and 7 − 4 = 3. Four facts from one family.
Step 2
Watch how
Two examples, worked out one step at a time.
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Family 5, 6, 11. What is 11 − 5?
5 + 6 = 11 and 6 + 5 = 11. Taking a part away gives the other part: 11 − 5 = 6 and 11 − 6 = 5.
Answer: 6 -
Family 2, 8, 10. What is 10 − 8?
2 + 8 = 10, so 10 − 8 = 2 and 10 − 2 = 8.
Answer: 2
Step 3
Play with it
Split a number into two parts. Slide to change them.
Step 4
Practice
Five questions. Think first. Then tap Show answer.
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3 + 7 = 10, so 10 − 7 = ?
Show answer
3
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6 + 9 = 15, so 15 − 9 = ?
Show answer
6
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4 + 5 = 9, so 9 − 4 = ?
Show answer
5
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7 + 8 = 15, so 15 − 8 = ?
Show answer
7
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Family 4, 8, 12. What is 12 − 4?
Show answer
8