Question

2000×199.9-1999×199.8（用简便算法和过程）

Answer 1

根据数字特点，把原式变为2000×199.9-199.9×1998，然后运用乘法分配律简算。
2000×199.9-1999×199.8
=2000×199.9-199.9×1998
=（2000-1998）×199.9
=2×199.9
=399.8

Answer 2

解
2000X199.9-1999X199.8
=2000X199.9-2000X199.8+199.8
=(2000X199.8-2000X199.8)+2000X0.1+199.8
=0+200+199.8
=399.8

Answer 3

=200x1999-1999x199.8
=1999x(200-199.8)
=1999x0.2
=(2000-1)x0.2
=400-0.2
=399.8

Answer 4

2000×199.9-1999×199.8
=200×1999-1999×199.8
=1999×(200-199.8)
=1999×0.2
=(2000-1)×0.2
=400-0.2
=399.8

Answer 5

解：原式=199.9*（2000-10*199.8）=（200-0.1）*2=400-0.2=399.8。