Rule of three (mathematics)

Okay, so you know how sometimes you have to do some math to figure out how much of something you need? Like if you wanted to make a cake and the recipe said you needed 2 cups of sugar, but you only had 1 cup, you might need to figure out how much of everything else you need to change to still make the cake taste good.

That's where the rule of three comes in. It's a way to figure out how much of one thing you need to change when you know how much of something else is changing. Basically, you can use three numbers and find out what the fourth number should be.

Here's an example: Let's say you have a recipe that makes 12 brownies, but you want to make 24 brownies instead. You can use the rule of three to figure out how much of each ingredient you need to double.

First, you write down what you know:

12 brownies requires:
- 1 cup of flour
- 1/2 cup of sugar
- 1/4 cup of cocoa powder

Then, you write down what you want:

24 brownies requires:
- ? cups of flour
- ? cups of sugar
- ? cups of cocoa powder

Now we use the rule of three to figure out what the missing numbers are. Here's how it works:

- You start with the number you know, which in this case is 12 brownies and 1 cup of flour.
- Then, you write down the number you want, which is 24 brownies and ? cups of flour.
- Next, you cross multiply: 12 times ? equals 24 times 1.
- Finally, you solve for the missing number: ? equals 2 cups of flour.

You can do the same thing for the sugar and cocoa powder:

- 12 brownies requires 1/2 cup of sugar, so 24 brownies requires 1 cup of sugar.
- 12 brownies requires 1/4 cup of cocoa powder, so 24 brownies requires 1/2 cup of cocoa powder.

So there you have it! You can use the rule of three to figure out how much of something you need to change when you know how much of something else is changing. Just remember to start with what you know, write down what you want, cross multiply, and solve for the missing number.