A method is disclosed for operating a microprocessor based reel-type slot machine. The payoff is randomly determined before any symbols are displayed. Two or more multiplier factors are randomly selected from separate predetermined groups. The factors are multiplied together to calculate the payoff. For each payoff, there are a predetermined number of symbol combinations corresponding thereto. One of the corresponding symbol combinations is randomly selected and displayed on the pay line. Zero payoffs are indicated by displaying a randomly selected losing combination.