35.9×69.3－68.3×35.8………………变一变,就简便.把69.3拆分成（68.3＋1）
=35.9×（68.3＋1）－68.3×35.8
=35.9×68.3＋35.9×1－68.3×35.8……………交换位置
=35.9×68.3－68.3×35.8＋35.9
=68.3×（35.9－35.8）＋35.9
=68.3×0.1＋35.9
=6.83＋35.9
=42.73