Fact Family vs. Number Family

Date: 09/24/2001 at 20:42:02
From: Marilee 
Subject: "Fact Family" vs. "Number Family"

I am trying to help my sister answer my nephew's question. We have all 
gotten quite clear on what a fact family is, but what seems to be left 
assumed, is that we just automatically then know what a number family 
is. We can't come up with a clear, simple answer to this. Please help.

Concerned Aunt and Parent

Date: 09/25/2001 at 08:44:02
From: Doctor Rick
Subject: Re: "Fact Family" vs. "Number Family"

Hi, Marilee.

I am not an elementary teacher, so I have not been trained to use 
these terms. I am a bit older than you, so I did not learn these terms 
in school, either. They are not terms used by mathematicians, but 
terms currently in vogue in the teaching of math. 

I have learned what "fact families" are through answering other 
students' and parents' questions. Fact families are explained in this 
item in our Dr. Math archives:

  Fact Families
  http://mathforum.org/dr.math/problems/atreacy.09.21.00.html   

A number family is an "extended family," while fact families 
are "nuclear families." A number family consists of all (addition) 
fact families that have the same largest number (sum). Thus, each 
column below is a fact family, and all the columns constitute the "6" 
number family:

  6+0=6   5+1=6   4+2=6   3+3=6
  0+6=6   1+5=6   2+4=6
  6-6=0   6-5=1   6-4=2   6-3=3
  6-0=6   6-1=5   6-2=4

I don't know how standard this terminology is. If what I have said 
doesn't fit with what you have seen, let me know and we'll try to 
figure out what your meaning is. Ideally all terms should be defined 
in a textbook when they are first used. This goes especially for 
pedagogical terms and others that parents cannot be expected to know. 
But I know that textbooks often are not ideal.

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