(1)3.78×0.8+3.78×0.2 =3.78×(0.8+0.2) =3.78×1 =3.78 (2)90.5×99+90.5 =90.5×(99+1) =90.5×100 =9050 (3)5×0.2×8×1.25 =(5×0.2)×(8×1.25) =1×10 =10 (4)8.57×103-8.57×3 =8.57×(103-3) =8.57×100 =857. (5)2.5×2.4 =2.5×4×0.6 =10×0.6 =6