Letters for numbers

Hello, and welcome to Myriora Maths! Think of a number, and add three. I don't know your number. But I can still write down what you did, using a letter! Let's see how.

Mathematicians use a letter for a number they don't know yet. Let's call your number n. Think of a number and add three: that's n add three.

We can write lots of things this way. Take away two: n take away two. Double it: two n. Halve it: n divided by two.

Two n means two times n. We leave out the times sign, because it looks too much like the letter x. So three n means three times n.

Now, if your number was five, we can work it all out. n add three is eight. And three n is three times five, which is fifteen.

Let's try one together. If n is four, what is two n add one? Say it out loud!

Two n is two times four, which is eight. Add one: nine!

Here's a question that catches lots of people. If n is five, what is three n? Some people write the three and the five next to each other, and say thirty-five. But three n means three times n. Three times five is fifteen!

Your turn! If n is six, what is four n take away three? Pick the right card. You've got twenty seconds, or pause the video. Go!

Time's up! Four n is four times six, which is twenty-four. Take away three: twenty-one!

Quick review. A letter can stand for a number we don't know yet. n add three means the number, add three. Three n means three times n. When we know the number, we can work it out. See you next time!