Fact Families

Date: 09/21/2000 at 14:17:20
From: Ann Treacy
Subject: Fact Families

What is a "fact family?"

Date: 09/21/2000 at 17:50:58
From: Doctor Rick
Subject: Re: Fact Families

Hi, Ann.

A fact family can be FOUR -- FOUR -- FOUR facts in one!

When you memorize an addition fact like 2 + 3 = 5, three other facts 
come along for free. The set (fact family) is

  2 + 3 = 5
  3 + 2 = 5
  5 - 2 = 3
  5 - 3 = 2

Some fact families have only two members. For instance,

  2 + 2 = 4
  4 - 2 = 2

Multiplication and division facts come in families in just the same 
way. For instance,

  3 * 5 = 15
  5 * 3 = 15
  15 / 3 = 5
  15 / 5 = 3

These are things we knew, but they didn't teach the term in school 
when I was a kid. It's a good term, though, I think.

- Doctor Rick, The Math Forum
  http://mathforum.org/dr.math/