0.8*0.6*6.5*12.5
=（0.8*12.5）*（0.6*6.5）
=10*3.9
=39
1.69*69-0.69*69
=(1.69-0.69)*69
=1*69
=69
8.5*100.2
=8.5*(100+0.2)
=850+1.7
=851.7
0.45*98
=0.45*(100-2)
=0.45*100-0.45*2
=45-0.9
=44.1