（1）原式=8+7.8+10.5

                =15.8+10.5

                =26.3（2）原式=70.72-35.604

                =35.116

（3）原式=0.38-0.17

                =0.21（4）原式=70.2-15.2

                =55

（5）原式=7.84+7.85

                =15.69（6）原式=20-15.28

                = 4.72

（7）原式=8.82-3.46

                =5.36（8）原式=27.87-22.94

                = 4.93