Interactive Ruby helps you to make complex computations without having to write a whole program.
Under linux type irb.

Ex1. calculate (10-7+500)*(4 power 3 )-square root of(900)

irb(main):001:0> (10-7+500)*(4**3)-Math.sqrt(900) => 32162.0

Ex2. get exact date at 14 days before now (in seconds 14x24x60x60 before now)

irb(main):002:0> Time.new - (14*24*60*60) => Thu Nov 21 15:52:53 +0100 2013