91乘31乘91简便运算（91乘以31用简便方法怎么算）

91X31x91

=91x91x31

=(90+1)(90+1)(30+1)

=(8100+90+90+1)(30+1)

=8281x(30+1)

=8281x30+8281

=8281x10x3+8281

=82810x3+8281

=(8000+2000+800+10)x3+8281

=24000+6000+1600+30+8281

=31630+8281

=31630+8000+200+80+1

=39830+80+1

=39911