3.6×2.8 =3.6×（3-0.2）=3.6×3-3.6×0.2=10.8-0.72=10.082.5×2.8 =2.5×（2+0.8）=2.5×2+2.5×0.8=5+2=73.9×2.8=3.9×（3-0.2)=3.9×3-3.9×0.2=11.7-0.78=10.92
