1991+199.1+19.91+1.991.
问题描述:
1991+199.1+19.91+1.991.
答
1991+199.1+19.91+1.991,=(2000-9)+(200-0.9)+(20-0.09)+(2-0.009),=(2000+200+20+2)-(9+0.9+0.09+0.009),=2222-9.999,=2222-(10-0.001),=2222-10+0.001,=2212.001.