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