999×9999×19999=?
1个回答

= (1000 - 1)(10000 - 1)(20000 - 1)

= (10000000 - 1000 - 10000 + 1)(20000 - 1)

= 200000000000 - 20000000 - 200000000 + 20000 - 10000000 + 1000 + 10000 - 1

= 200000000000 - 200000000 - 30000000 + 30000 + 999

= 199800000000 - 30000000 + 30999

= 199770030999