For what it is worth: here is an example of a non-uniform random variate:

  a = [0,0,0,0,0,0,0,0,0,0]
  1000.times do
    a[5 *(rand + rand)] += 1
  end

results in (actual numbers may vary randomly):

  irb(main):020:0> a
  => [28, 60, 96, 151, 171, 168, 146, 96, 63, 21]