Worthy of a snippet in its own right as well as a smaller part of this snippet. Full detail on its use is here, but it is a way of returning a random true or false based on the odds.

class Odds
  def self.true?(chance=0)
    (rand(chance)<1)
  end
end

For example for 1 in 4 odds you would call

  Odds.true?(4)

For a dead cert true? or true?(0) would always return true. Check out the other links for a slightly modified version which is optimised for known low failure rates.