While adding numbers we can procede on a large pile of them but to do substruction it is better to do it in twos. It can be done by adding all negative ones (to be substructed) all together first. Example: 3745-740-1020-15= 745-(740+1020+15).
It is presumed that the substruction algorithm differ significantly from that of addition but it is not the case. Off cours intead of adding digits we substruct them and instead of adding carries we substruct the as well. If we understand this process both algorithms seems to be identical.
So to get the result of any given substruction we write the number to be substruct under the one which we have to substruct from then we substruct consecutively the digits in columns starting with the first on the righr, means units and write down the results under the bottom line.
If the top digit is to small we add 10 to it and write down the result.
This ten is our decimal carry take off course from the next column on the left so if we want to write it as usual on the top of the pile we do it by puting -1 above the next column.
If you prefer to remember that you have take 1 from the next column without writting it it is OK too.
So you repet this procedure for all columns one after an other remembering or writting our negative carries.
Doing our exercices you will try to remember them to train your memory but if you want to exercise writing click [HELP].
Enjoy!
designed by Witold Wojcik