(1)( 7.8/3.9)*3.4=2*3.4=6.8
(2) (85/5)/0.17=17/0.17=0.01
(3) (0.125*2.4+0.125*0.8)*2.5= (0.3+0.1)*2.5=0.4*2.5=1
(4) (10-0.1)*9.9=10*9.9-0.1*9.9=99-0.99=98.01
(5) 17.3*(10-0.1)+1.73=10*17.3-17.3*0.1+1.73=173
(6) 8.5*(100-4)+34=100*8.5-8.5*4+34=850
(7) (1+0.1)+(2+0.1)+(3+0.1)+(4+0.1)+(5+0.1)=(1+2+3+4+5)+5*0.1=15.5
(8) 99.9*(999+1+1)=99.9*(1000+1)=99.9*1000+99.9=99900+99.9=99999.9
(9)(3*1.5*3*2.5*2*2.4)/(1.5*2.5*2.4)=3*3*2=18
(10)(3/4)*(66+34)=(3/4)*100=75
*乘 /除