解:6.8 x 0.1 + 0.5 x 68 + 0.049 x 680= 68 x 0.01 + 68 x 0.5 + 68 x 0.49= 68 x (0.01 + 0.5 + 0.49)= 68 x (0.5 + 0.5)= 68 x 1= 68
=68*(0.1*0.1+0.5+0.049*10)=68*(0.01+0.5+0.49)=68*1=68求采纳!