398×2556×199+56怎么简算

398×2556×199+56
=400X2556×199-2X2556X199+56
=400X2556X200-400X2556-400X2556+2X2556+56
=80000X2556-800X2556+2X2556+56
=79202X2556+56
=39601X5000+79202X56+56
=198005000+79203X56
=198005000+79203X60-79203X4
=198005000+4752180-316812
=202440368
虽然尽量用个位数相乘,但还是很容易出错的

398×25
=(400-2)*25
=400*25-25*2
=10000-50
=9950
56×199+56
=56*(199+1)
=56*200
=11200