1/7×5/12+5/12÷7/5 =1/7×5/12+5/12×5/7 =5/12×(1/7+5/7) =5/12×6/7 =5/14 15÷9×5/9 =15/9×5/9 =25/27 17/35×36 =17/35×(35+1) =17/35×35+17/35×1 =17+17/35 =17又17/35