Fact families

Hello, and welcome to Myriora Maths! Three numbers can make a family. If you know one fact, you get three more for free! Let's see how.

Here are three red counters, and five blue counters. Together they make eight. Three, five and eight are a family. Eight is the whole. Three and five are the parts.

We can add the parts in either order. Three plus five is eight. Five plus three is eight too.

Now take a part away from the whole. Eight take away five leaves three. Eight take away three leaves five. That's four facts from one family!

Why does this work? Adding five puts the parts together. Taking five away pulls them apart again. So minus undoes plus.

This family trick helps with take aways. What is twelve minus nine? Think: nine plus what makes twelve? Nine plus three is twelve. So twelve minus nine is three.

Let's try one together. Four, six and ten are a family. Can you say all four facts? Say it out loud!

Four plus six is ten. Six plus four is ten. Ten take away six leaves four. Ten take away four leaves six. Well done!

Here's a question that catches lots of people. Write a take away fact for the family three, five and eight. Some people write three minus eight equals five. But you can't take eight cookies away from three cookies! When you take away, the whole goes first: eight minus three equals five.

Your turn! Two plus seven is nine. Which fact is in the same family? Pick the right card. You've got fifteen seconds, or pause the video. Go!

Time's up! The family is two, seven and nine. Nine is the whole. Take seven away from nine, and two is left. So nine minus seven equals two!

Quick review. Two parts and a whole make a family. One fact gives you four: two adds and two take aways. And you can use adding to work out a take away. See you next time!