Rather than a simple one-liner, I figured I'd take the time to develop a test case and a full set of classes.

Another Lucky 13 Entry

require 'open-uri'
require 'test/unit'

class Spin
  def self.winning_number
    URI.parse('http://roulette.engineyard.com').read.gsub(/[^\d]/,'').to_i
  end
end

class StraightBet
  attr_accessor :winning_number
  
  def initialize(number,bid)
    @number = number
    @bid = bid
  end
  
  def payout
    if @number == @winning_number
      @bid * 35 
    else
      0
    end
  end
end

bid = StraightBet.new(13,100_00)
bid.winning_number = Spin.winning_number
puts "Your payout: #{bid.payout}"

class Lucky13Test < Test::Unit::TestCase
  def setup
    @bid = StraightBet.new(13,100_00)
  end
  
  def test_the_ball_falls_on_lucky_13
    @bid.winning_number = 13
    assert_equal(3500_00, @bid.payout)
  end
  
  def test_the_ball_does_not_fall_on_luck_13
    @bid.winning_number = 15
    assert_equal(0_00, @bid.payout)
  end  
end