Example script that calculates the probability of getting each score in a "roll 4 six sided dice, drop the lowest, then sum" scheme.

4d6drop.rb

#!/usr/local/bin/ruby
# Calculates the distribution of 4d6, drop lowest

scores = {}
(1..6).each do |i|
  (1..6).each do |j|
    (1..6).each do |k|
      (1..6).each do |l|
        dice = [i, j, k, l].sort
        dice.shift
        score = dice.inject :+
        scores[score] ||= 0
        scores[score] += 1
      end
    end
  end
end

scores.each do |k, v|
  puts "#{k}\t#{v}"
end