4321×1234-4322×1233
=4321×1234-4321×1233-1333
=4321×（1234-1233）-1333
=4321-1333
=2988
7.2×61.3+73.8×2.8
=7.2×61.3+61.3×2.8+12.5×2.8
=61.3×（7.2+2.8）+12.5×8×0.4
=61.3×10+100×0.4
=613+40
=653