0.6÷[2又1/2-(2/3+0.25)×0.6]=3/5÷[5/2-(2/3+1/4)×3/5]=3/5÷[5/2-(2/3×3/5+1/4×3/5)]=3/5÷[5/2-(2/5+3/20)]=3/5÷(5/2-11/20)=3/5÷39/20=3/5×20/39=4/13
