The Dow Jones industrial average posted modest gains on Friday but ended down 67 points, finishing the shortened holiday week at 10,213. In Friday trading, General Electric provided a boost when its second-quarter results beat forecasts. Investors remained jittery as they looked forward to a new round of earnings reports this week, when they begin in earnest. In ad-related stock news, Grey Global Group, which is considering a possible sale, saw its share price fluctuate between $940 and $965 throughout the week, closing Friday at $949.97. On the Big Board, Omnicom shares fell sharply during the week, dropping 4.1 percent to close at $69.93 (see Hotlines). IPG’s stock price ended down 0.2 percent to $13.08. WPP, trading as American Depository Receipts on the Nasdaq, declined 3.2 percent to finish at $49.07.