Berkshire Hathaway gains at open as stock to be added to S&P 500

Berkshire Hathaway Inc shares gained at the open on Friday as investors were optimistic about the stock's coming addition to the S&P 500 index <.SPX> after the close.

The stock opened 0.7 percent higher at $77.22.

(Reporting by Angela Moon; Editing by James Dalgleish)