As the economy revs up, some jobs are growing at a fast clip, while other positions are falling by the wayside, according to the career website Zippia. And while some occupations may not be the fastest growing, there are about three dozen positions that are so prevalent that they each continue to be occupied by millions of workers -- the top being retail salespersons, food preparers working under chefs and cooks, cafeteria and fast-food servers, cashiers, office clerks and registered nurses. Related: 10 ways to reach job seekers in the digital age Zippia analyzed data from the Bureau of Labor Statistics to find which jobs are growing in demand, and which are fast dropping in numbers – and the federal agency explains what is accounting for both trends.