Stocks were mixed on Monday morning as investors weighed a new round of earnings reports and awaited key inflation data later this week. Tyson Foods shares fell more than 6% after the company posted weak fiscal 3Q sales and earnings and announced that it would close four poultry plants. On the positive side, Berkshire Hathaway shares rose 3% on a 6% increase in second-quarter income, helped by higher investment income and strength in the company's insurance hol