All from 9 last from 10 - First extension

If you want to this subtraction:-
600 - 77. Do the following first,By one less then the one before applied to the 6, this gives 5. Then apply the sutra all from 9 and last from 10 to give 524.
So 5,000 - 123 = 4877.
This is very good to check your change:- You buy something for £3.46 with £20.00 what is your change.Answer £16.54.
Try this yourself:-
8000 - 3222. Remember we are taking more then 3,000 away so 4 will be left in the thousand coulmn. The answer is 4778.