# Working with Numbers

In order to start `irb`

open your terminal and type `irb`

, then hit the
`return`

key (`enter`

). In order to quit `irb`

again (and get back to your
system shell prompt) you can type `exit`

or press `ctrl-d`

, which does the
same.

## Exercise 1.1

In `irb`

, calculate:

- How many hours are in a year.
- How many minutes are in a decade?
- How many seconds old are you?

## Exercise 1.2

What do you think happens when you combine the following floats and integers?

Try computing these in `irb`

:

`3.0 / 2`

`3 / 2.0`

`4 ** 2.0`

`4.1 % 2`

Is the result a float or an integer?

## Exercise 1.3

Methods are a way of “doing something with an object”. E.g. in Ruby, numbers have two methods that allow you to check whether the number is odd or even.

Look through the documentation for integer
numbers (called `Fixnum`

) and find the methods that tell if a number is odd or
even.

## Exercise 1.4

In `irb`

, use these methods to find out if certain numbers are odd or even.
Numbers like `0, 1, 2, 99, -502`

etc.

You can use a method by appending a dot `.`

and then the method name
to the object. E.g. `-99.abs`

uses (we also say: “calls”) the method
`abs`

on the number `-99`

.

Try for yourself what it does, and google for “ruby abs” to find the documentation for this method.