How many ways can 4 students be arranged in a row?
Let's say they're going to be sat on chairs, numbered
To start with, the students are stood off to the side and you have to sit them on the chairs.
No matter which student you choose, you will sit a student on the chair and have
Now again, no matter who you choose, you have
Now you'll sit the last one down on the last chair - there's only
In probability, when you have certain numbers of possibilities for a certain number of events, you multiply the numbers of possibilities, so you have
This is also known as