Using a letter for an unknown number

A bakery packs kaya buns into boxes. Every box holds the same number of buns. There is 1 box, and 3 more buns beside it. Write how many buns there are altogether. We can't put a number on it. Nobody has counted what's inside the box. We can still write it, if we give that number a name. You've drawn a blue block like this before. In the ratio videos, we called it 1 unit. In algebra, we give it a letter. n stands for the number of buns in 1 box. n isn't the box. n is how many buns are inside it. Now we can answer it. Blue is the number we don't know. Purple is the number we do. So altogether, that's n plus 3 buns.

Here's a new question. There are 3 boxes. Write how many buns there are altogether. Each box holds n buns, so that's n plus n plus n. 3 groups of n is 3 times n. We write that as 3 n. The 3 goes in front, and the times sign is left out. And 3 n counts buns, not boxes.

Another new question. The buns from 1 box are packed equally into 3 bags. Write how many buns are in each bag. 3 bags, so we cut the block into 3 equal pieces. Each bag gets n divided by 3. We can write that division as a fraction too. n over 3. Both mean the same thing, and the fraction is the one you'll see most.

Your turn. A bakery packs kaya buns into boxes. Every box holds n buns. There are 4 boxes, and 2 more buns beside them. Write how many buns there are altogether. Try it first. Pause if you like. Each box holds n buns, and there are 4 boxes. So that's 4 n. Then 2 more buns. Altogether, 4 n plus 2 buns. Nobody counted what was inside the box. We gave that number a name instead. And then we could add to it, multiply it, and share it out, just like any other number.