“What the heck is a fact family?” I asked the first time I read the term.
And the second, third, fourth and fifth times.
“Fact families” – both the term and the families – seem to be everywhere these days.
So what IS a fact family?
Well, it’s a family of facts. But not parents or cousins. More like siblings.
Here’s a nice one I’ve known for years:
And here’s another one I’m fond of:
Is that a real thing in math?
The short answer is “no.”
When you look it up on WolframAlpha.com, you don’t get a definition. It gives you the definition of “family.”
And according to that definition, any collection of facts (totally random, even) can be a “fact family.”
So is it a real thing?
The long answer is “yes.”
A nice little collection of related facts is called a fact family.
But sometimes we get even sloppier and say that 8, 3 and 5 are a fact family. The numbers aren’t the facts, but, as grownups, we know what we mean.
I’ve mentioned a number of times that mathematicians just make this crap up. So even WE can play a mathematician and create…
A Formal Definition bum-bum-buum
Ahem… pardon me while I geek out a moment…
Let be a group and , and in so that . Then we say , and form a fact family and we can write
A Casual Definition
We can call any three numbers , and , that make , a fact family. And we know that not only does , but also and .
Likewise with multiplication, we can call any three numbers , and , that make , a fact family. And we know that not only does , but also and .
So there you have it. Fact Family formally and casually defined.
I feel so much better. 🙂
You might also like:
- Math Words – Start Using Them Early
- Hanukkah Math – Playing the Dreidel Game
- Why Most People Say They Hate Math
- Family Math Night – Nachos & Numbers
This post may contain affiliate links. When you use them, you support us so we can continue to provide free content!