0.9+0.99+0.999+0.9999怎么简便计算

原式=1-0.1+1-0.01+1-0.001+1-0.0001
=4-0.1111
=3.8889

(1+1+1+1)-(0.1+0.01+0.001+0.0001
=4-0.1111
=3.8889

0.9+0.99+0.999+0.9999
=(1+1+1+1)-(0.1-0.01-0.001-0.0001)
=4-0.1111
=3.8889

=0.9+0.99+0.999+0.9999+(0.1+0.01+0.001+0.0001)-(0.1+0.01+0.001+0.0001)
=1+1+1+1-(0.1+0.01+0.001+0.0001)
=4-0.1111
=3.8889

与上几个解法看似相似，其实原理不同。

0.9+0.99+0.999+0.9999
=(1-0.1)+(1-0.01)+(1-0.001)+(1-0.0001)
=4-0.1-0.01-0.001-0.001
=4-0.1111=3.8889
就是这一种最简单啊

0.9+0.99+0.999+0.9999
=9*(0.1+0.11+0.111+0.1111)
=9*0.4321
=3.8889