Oct 28 (Reuters) - CME Group, the world’s biggest futures exchange operator, on Wednesday said its third-quarter profit plunged 35% as decreased trading volumes resulted in lower fees for clearing and settling transactions. Net income for the three months ended Sept. 30 came in at $411.5 million, or $1.15 per share, compared with $636.3 million, or $1.78 per share, last year.