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

4000000+400000+40000+4000+400+40+10-7=4444443

=(3999999+1)+(399999+1)+(39999+1)+(3999+1)+(399+1)+(39+1)+(9+1)-7
=4444440-7=4444433

3999999=4000000-1
399999=400000-1
同理
上市和为4444444-6+10-1=4444447

4000000-1+400000-1+40000-1+4000-1+400-1+40-1+10-1=4444440+10-7=4444443

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

3999999+399999+39999+3999+399+39+9
=4000000+400000+40000+4000+400+40+3
=4444443