问一道计算题

题目

问一道计算题
3999999+399999+39999+3999+399+39+9
请把过程写下来!要求巧算!

答案

3999999+399999+39999+3999+399+39+9
=4000000-1+400000-1+40000-1+4000-1+400-1+40-1+10-1
=44444450-7
=44444443