Hi Osito....

Fact families usually have four equations or number sentences.  Addition/subtraction fact families have two addition number sentences and two subtraction number sentences.  Multiplication/division fact families have two multiplication number sentences and two division number sentences.  For example:

3 + 4 = 7
4 + 3 = 7
7 - 4 = 3
7 - 3 = 4

Or

4 x 5 = 20
5 x 4 = 20
20 / 5 = 4
20 / 4 = 5

However, there are some fact families with only two number sentences.  This is when there are same digit numbers in the sentence.  For example:

4 + 4 = 8
8 - 4 = 4

Or

5 x 5 = 25
25 / 5 = 5

Hope this helps!

Vicki