Key TakeawaysShares of Palantir Technologies, Dell Technologies, and Erie Indemnity all gained Monday morning after it was announced they were being added to the S&P 500.Shares of firms included in the S&P 500 often get a bounce because they are purchased by investors who put their money in S&P 500 index funds.The companies will be replacing American Airlines Group, Etsy, and Bio-Rad Laboratories. Shares of Palantir Technologies (PLTR), Dell Technologies (DELL), and Erie Indemnity (ERIE) all gained Monday m ...