-1/2-5又1/5-1+3又1/4-4.5+2又1/3
=-5-1+3又1/4-4.5+2又1/3
=-6-4.5+3又1/4+2又1/3
=-10又6/12+3又3/12+2又4/12
=-7又3/12+2又4/12
=-411/12