Dollar General joins Standard & Poor's 500 index

Associated Press

NEW YORK (AP) — Dollar General Corp. will replace Cooper Industries PLC to join the S&P 500 after the close of trading on Friday.

The S&P Dow Jones Indices, which manages the iconic market index, said Monday that the move comes as a result of Eaton Corp.'s plans to acquire Cooper Industries in a deal expected to be completed at that time.

Dollar General, based in Goodlettsville, Tenn., is a discount retailer with more than 10,000 stores in 40 states. Its shares fell 10 cents to close at $49.41 Monday. The stock gained $1.69, or 3.4 percent, to $51 in aftermarket trading following the announcement.

Stocks typically gain when they added to indices, because mutual funds and other institutional investors that track those indices are expected to update their portfolios by purchasing shares of the newly added companies.