原式=[31/2-(5/4÷5/3+7/2)]÷(-9/8)=[31/2-(5/4×3/5+7/2)]×(-8/9)=[31/2-(3/4+7/2)]×(-8/9)=(31/2-17/4)×(-8/9)=45/4×(-8/9)=-10
答案是-10
