Question

3.9+0.39+0.09+0.0039+0.00039简便运算怎么算

算式的简便算法
3.9+0.39+0.039+0.0039+0.00039的简便算法
快,用递等式,如：
98+998+9998
=100+1000+10000+2*5
=1111100-10
=1111090

Answer 1

3.9+0.39+0.039+0.0039+0.00039
=4-0.1+0.4-0.01+0.04-0.001+0.004-0.0001+0.0004-0.00001
=4.4444-0.11111
=4.3333-0.00001
=4.33329