Order doesn't matter

Hello, and welcome to Myriora Maths! What is seven, plus eight, plus three? There's a clever way to do it in your head. Let's find out!

First, when we add two numbers, the order doesn't matter. Three plus five is eight. Five plus three is eight too. It's the same counters, just looked at from the other side.

Why? Adding just puts things together. It doesn't matter which group goes down first. The total is the same.

And with three numbers, we can add any two first. Seven plus eight is fifteen, and fifteen plus three is eighteen. Or, eight plus three is eleven, and eleven plus seven is eighteen. The same answer!

So here's the clever part: look for pairs that make ten. Seven plus three is ten. Ten plus eight is eighteen. That's much easier!

Let's try one together. What is six, plus nine, plus four? Here's a tip: look for a pair that makes ten. Say the answer out loud!

Six plus four is ten. Ten plus nine is nineteen. Well done if you said nineteen!

It works with bigger numbers too. Twenty-eight, plus fifteen, plus twelve. Twenty-eight and twelve make forty. Forty plus fifteen is fifty-five!

Here's a question that catches lots of people. Is ten take away three the same as three take away ten? Some people say yes, because order doesn't matter. But that rule is only for adding! Ten take away three is seven, but you can't take ten sweets away from three sweets.

Your turn! What is three, plus eight, plus seven, plus two? Pick the right card. You've got fifteen seconds, or pause the video. Go!

Time's up! Three plus seven is ten. Eight plus two is ten. Ten plus ten is twenty!

Quick review. When you add, the order doesn't matter. Look for pairs that make ten, and add those first. But with taking away, the order does matter. See you next time!