You already know how to use number families to write one addition fact and one subtraction fact. That's excellent! Now you can use what you've learned to complete number families. A complete number family will give you two addition facts and two subtraction facts.
Look at this number family:
Can you give one addition fact for this number family? Right, 3 plus 5 equals 8 (3 + 5 = 8) is one addition fact. You find it by looking at the numbers from left to right along the arrow. This number family gives us another fact, 5 plus 3 equals 8 (5 + 3 = 8). You still end with the greatest (larger) number, but the order of the lesser (smaller) addends(numbers added together) changes.
Now let's write two subtraction facts for a new number family.
One subtraction fact for this number family starts with the greatest number and goes backward along the arrow. What is it?
You're right! It's 9 minus 5 equals 4 (9 - 5 = 4). The other subtraction fact also starts with a greatest number, but the order of the lesser numbers changes. Can you guess the second fact? If you said 9 minus 4 equals 5 (9 - 4 = 5), you're right.
Here's a new number family:
Let's write two addition facts and two subtraction facts for this family. Remember, one addition fact goes forward along the arrow. The other addition fact also equals the greatest number. If we follow these rules, the two addition facts for this family will be 3 plus 4 equals 7 (3 + 4 = 7) and 4 plus 3 equals 7 (4 + 3 = 7).
To write the two subtraction facts, we have to start with the greatest number and go backward along the arrow. The other subtraction fact also starts with the greatest number. So the two subtraction facts for this family are 7 minus 4 equals 3 (7 - 4 = 3) and 7 minus 3 equals 4 (7 - 3 = 4).
You've just written two addition facts and two subtraction facts. Good job!
