12.5*(8-0.8)
=12.5*8-12.5*0.8
=100-10
=90
2.7*4.3+5.7*2.7
=2.7*（4.3+5.7）
=2.7*10
=27
0.77*99
=0.77*100-0.77
=77-0.77
=76.23
6.18*9.9+0.618
=0.618*99+0.618
=0.618*（99+1）
=0.618*100
=61.8
0.25*1.25*0.8*40
=（0.25*40）*（1.25*0.8）
=10*1
=10