漏了加号了吧
(-9.8)-(-5.2)+(-0.1)-(-8.4)+(+4.8)
=-9.8+5.2-0.1+8.4+4.8
=-4.6-0.1+8.4+4.8
=-4.7+8.4+4.8
=3.7+4.8
=8.5