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.