数学简算题！答会必踩！

1.
0.9+0.99+0.999
=1-0.1+1-0.01+1-0.001
=3-0.111
=2.889
2.
9999+9998+9997+9996
=10000-1+10000-2+10000-3+10000-4
=40000-10
=39990

1. 2.889
2. 39990

这道应该不是难题啊,你要学会掌握方法,比如凑整,凑十法.
1. 0.9+0.99+0.999
=(1-0.1)+(1-0.01)+(1-0.001)
=3-0.111
=2.889

2. 9999+9998+9997+9996
=(10000-1)+(10000-2)+(10000-3)+(10000-4)
=40000-10
=39990
或者可以这样做
9999+9998+9997+9996
=9999+9998+9997+9990+6
=9999+1+9998+2+9997+3+9990
=39990

9999+9998+9997+9996
=10000-1+10000-2+10000-3+10000-4
=40000-10
=39990 对吗

(0.9+0.1)+(0.99+0.01)+(0.999+0.001)-0.111
（9999+1）+（9998+2）+（9997+3）+（9996+4）-10

1.
0.9+0.99+0.999
=1+1+1-(0.1+0.01+0.001)
=3-0.111
=2.889
2.
9999+9998+9997+9996
=10000*4-(1+2+3+4)
=40000-[(1+4)*2]
=40000-10
=39990