Number families are groups of three numbers, two small and one big, that are used to form two addition and two subtraction equations. Students learn that when the big number is missing, they must add the two small numbers together to find the solution, but when a small number is missing they must subtract the small number from the big number to find the solution.

Copyright: 2001

Grades: Gr. 3 - Gr. 5

**Citation (MLA)**
*Lesson 3: Number Families*.
Prod. Math Mastery. Math Mastery, 2001.
*Discovery Education*. Web. 18 September 2014. <http://www.discoveryeducation.com/>.

**Citation (APA)**
Math Mastery (Producer).
(2001).
*Lesson 3: Number Families*. [TitleChapter].
Available from http://www.discoveryeducation.com/

**Citation (Chicago Manual of Style)**
Math Mastery. "Lesson 3: Number Families."

Discovery Education: http://streaming.discoveryeducation.com/