S&P 500 to add chemicals maker FMC, drop Centex

NEW YORK Aug 11 (Reuters) - Standard & Poor's on Tuesday said FMC Corp (FMC.N), a maker of pesticides and agricultural chemicals, will replace Centex Corp (CTX.N) in its flagship S&P 500 stock index .SPX after the close of trading on August 18.

Centex is being removed because it is being acquired by another home builder, Pulte Homes Inc (PHM.N), which is also in the S&P 500. FMC is based in Philadelphia.

Shares of companies joining the S&P 500 often rise because many portfolio managers try to track the index and must buy shares of companies that enter it.

FMC shares closed Tuesday up 11 cents at $49.75 on the New York Stock Exchange. Price quotations following S&P's after-hours announcement were not immediately available. (Reporting by Jonathan Stempel; Editing by Steve Orlofsky)