3.8乘以4.5+6.2乘以4.9 =3.8乘以4.5+6.2乘以(4.5+0.4) =3.8×4.5＋6.2×4.5＋6.2×0.4 =（3.8＋6.2）×4.5＋2.48 =10×4.5＋2.48 =45+2.48 =47.48
