Question

1999+199.9+19.99+1.999+2.111怎么算简便

Answer 1

（2000-1）+（200-0.1）+（20-0.01）+（2-0.001）+(2+0.111)

=2000+200+20+2+2+0.111-0.1-0.01-0.001-1

=2224-1

=2223