=999×(101 × 99 +1)
=999 ×10000
=999 0000
101×99×999+999
=【(100+1)×99】×999+999×1
=【100×99+1×99】×999+999×1
=【9900+99】×999+999×1
=9999×999+999×1
=(9999+1)×999
=10000×999
=9990000
=(100+1)*(100-1)*999+999
=(10000-1)*999+999
=9990000
101*99*999+999
=999*(101*99+1)
=999*(100*99+99+1)
=999*(9900+100)
=999*10000
=9990000