Results of Operations The following table presents selected financial information derived from our consolidated statements of income expressed as a percentage of sales for the years indicated. Year Ended December 31, 2013 2012 2011 Sales Carrier Networks Division 78.0% 79.3% 79.4% Enterprise Networks Division 22.0 20.7 20.6 Total sales 100.0% 100.0% 100.0% Cost of sales 51.9 49.0 42.2 Gross profit 48.1 51.0 57.8 Selling, general and administrative expenses 20.2 21.7 17.4 Research and development expenses 20.4 20.3 14.0 Operating income 7.6 9.1 26.4 Interest and dividend income 1.1 1.2 1.1 Interest expense (0.4)  (0.4)  (0.3)  Net realized investment gain  1.3 1.5 1.7 Other income (expense), net  (0.1)  — (0.1) Gain on bargain purchase of a business  — 0.3 — Income before provision for income taxes 9.5 11.8 28.7 Provision for income taxes (2.3)  (4.1)  (9.4)  Net income 7.1% 7.6% 19.3% ADTRAN 2013 Annual Report 22