2.(1) 21/4-(-1.5)+(-5/3)=21/4+6/4-5/3=61/12
(2)(-8)+(-11)-13+(-12)=-8-11-13-12=-44
4.(1)50-11-21+41+89-72+86-54-12=96吨
(2)-11-21+41+89-72+86-54-12=46t
5.(1)60 (2)-1.5 (3)-7/25 (4)6.4
6.(1)-10.2 (2)-4 (3)-28 (4)9/4
7(1)81 (2)-0.027 (3)9/49 (4)100000(5)-1 (6)4/9
8.(1)5708000=5.708x10的6次
(2)4600000000=4.6x10的9次