One bond gives you four number sentences. They all use the same three numbers.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
A family of facts
If you know 3 + 4 = 7, you already know 7 − 3 = 4.
7
3
4
- 3 + 4 = 7
- 4 + 3 = 7
- 7 − 3 = 4
- 7 − 4 = 3
All four use the same three numbers: 3, 4, and 7.
First part
Second part
Why exactly four sentences
Two additions from swapping the parts, and two subtractions from removing each part in turn. Three numbers cannot make more than that.
Use the easy one to answer the hard one
Stuck on 12 − 5? Ask what goes with 5 to make 12. Same family, easier question.
Step 2: Try It Yourself
Change the parts and watch all four change with them.
7
2
5
- 2 + 5 = 7
- 5 + 2 = 7
- 7 − 2 = 5
- 7 − 5 = 2
All four use the same three numbers: 2, 5, and 7.
Step 3: Watch an Example
One step at a time.
Watch Ben Use One Fact
Ben already knows 5 + 2 = 7. He is asked for 7 − 5.
- Step 1
He does not count. He looks at the numbers.
Step 4: Your Turn
Practice makes it stick.
Using What You Know
Problem 1 of 1
You know 6 + 3 = 9. What is 9 − 6?
Build a Family
Make a family where both parts are the same. What do you notice?
8
4
4
- 4 + 4 = 8
- 8 − 4 = 4
4 and 4 are the same, so this family has only two facts, not four.
Step 5: Quick Check
Show what you know.
Question 1 of 2
You know 4 + 5 = 9. What is 9 − 4?
Question 2 of 2
How many different sentences does 4 and 4 make?
What You Learned
- Three numbers make a family of facts.
- Adding and subtracting are the same relationship.
- A double makes only two sentences, not four.