12.5/3.6一7/9+8.3/3.6＝ 12.5/3.6+8.3/3.6—7/9＝20.8/3.6-7/9＝52/9-7/9＝45/9＝5第二种算法:
12.5/3.6一7/9+8.3/3.6＝ 12.5/3.6—2.8/3.6+8.3/3.6＝（12.5+8.3-2.8）/3.6＝18/3.6＝5