0.5+(-1)/4-(-2.75)+1/2
=（0.5+0.5）+(2.75-0.25)
=1+2.5
=3.5
(-2/3)+(-1/6)-(-1/4)-1/2
=-2/3-1/6+1/4-1/2
=-8/12-2/12+3/14-6/12
=-13/12
如果本题有什么不明白可以追问,