如题所述
第1个回答 2021-08-05
21*99
=21*(100-1)
=21*100-21
=2100-21
=2079
=21*(100-1)
=21*100-21
=2100-21
=2079
第2个回答 2021-08-05
=(20+1)×99
=20×99+99
=1980+99
=1979+1+99
=1979+100
=2079
=20×99+99
=1980+99
=1979+1+99
=1979+100
=2079
第3个回答 2021-08-05
21×99
=21×(100-1)
=21×100-21×1
=2100-21
=2079
=21×(100-1)
=21×100-21×1
=2100-21
=2079
第4个回答 2021-08-05
21x99
=21x(100-1)
=21x100-21x1
=2100-21
=2079
=21x(100-1)
=21x100-21x1
=2100-21
=2079
第5个回答 2021-08-05
21ⅹ99=21x100-21=2100-21=2079