999×99×9巧算,
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999×99×9巧算,
![999×99×9巧算,](/uploads/image/z/18157127-23-7.jpg?t=999%C3%9799%C3%979%E5%B7%A7%E7%AE%97%2C)
999×99×9
=(1000-1)*(100-1)*(10-1)
=(10^5-1100+1)*(10-1)
=(10^5-1099)*(10-1)
=10^6-10^5-10990+1099
=900000-9891
=890109
=(1000-1)*(100-1)*(10-1)
=(10^5-1100+1)*(10-1)
=(10^5-1099)*(10-1)
=10^6-10^5-10990+1099
=900000-9891
=890109