原式=-1/4+16/5-3/4-11/5
=(-1/4-3/4)+(16/5-11/5)
=-1+1
=0
7又1/5-0.5-8+2.8+1/2-5.6+6-4.4
=7.2-0.5-8+2.8+0.5-5.6+6-4.4
=(7.2+2.8)-8+(0.5-0.5)-(5.6+4.4)+6
=10-8+0-10+6
=6-8
=-27又1/5-0.5-8+2.8+1/2-5.6+6-4.4=