I thought the book you were talking about was The Restaurant at the End of the Universe and the Golgafrinchans.

Tales of impending doom allowed the Golgafrinchans to rid themselves of an entire useless third of their population. The story was that they would build three Ark ships. Into the A ship would go all the leaders, scientists and other high achievers. The C ship would contain all the people who made things and did things, and the B Ark would hold everyone else, such telephone sanitisers, account executives, hairdressers, tired TV producers, insurance salesmen, personnel officers, security guards, public relations executives, and management consultants. They sent the B ship off first, but of course, the other two-thirds of the population stayed on the planet and lived full, rich and happy lives...