# Numbers

Clojure has several different types of numbers.

- Integer - are positive and negative whole numbers, including zero.
- Float - decimal numbers, like the value for Pi, 3.141
- Ratio - we know these as fractions, eg 1/3, 22/7

You write them in Clojure just like we do in every day life.

```
0
12
-42
0.072725
10.5
-99.9
;; To maintain precision we can represent fractions, called ratio types
13/7
2/3
```

Numbers can be used by themselves, although they don't do anything useful alone. So lets do some maths...

### Immutable values

Numbers are an example of Immutable values. Immutable means a value cannot change once used.

How do we change anything then? We can pass numbers to functions and get a new number as a result.

It would difficult to understand the world if anyone could randomly change the value of 1 to equal another number. We couldn't say for definite how many things we had.

The opposite of Immutable is mutable.