It's a Living S02E12 - Horsing Around

During dinner service one night at Above The Top, Jan overhears a jockey and a gambler fix a horse race by making horse No. 2 as the "winner" of the race in question.  So Jan and Maggie decide to each make a bet on horse No. 2 at the racetrack the next day and the both of them win their respective bets of $100 and $10 each(Jan wins a cool $1,000 while Maggie wins $100).  After telling the other girls and Sonny about their recent fortune, Jan and Maggie make another bet on another horse after they overhear the same jockey and gambler make another fix.  At the racetrack the next day, Maggie overhears the gambler make a bet on another horse and tells the gang, including Nancy, who invites herself over after Sonny tried to borrow some money from her for the race, that they made a mistake, but the horse that they betted on wins the race by pure dumb luck.