这两道题怎么简算?

问题描述:

这两道题怎么简算?
(1)999×1999
(2)20000÷12.5÷25÷0.8÷4

(1)999×1999
=(1000-1)×1999
=1000×1999-1×1999
=1999000-1999
=1997001
(2)20000÷12.5÷25÷0.8÷4
=20000÷(12.5×25×0.8×4)
=20000÷[(12.5×0.8)×(25×4)]
=20000÷[10×100]
=20000÷1000
=20