1999+199.9+19.99+1.999+0.

1999+199.9+19.99+1.999+0.1999

3个回答

1999+199.9+19.99+1.999
=2000-1+200-0.1+20-0.01+2-0.001
=2000+200+20+(2-1-0.1-0.01-0.001)
=2220+0.889
=2220.889