Looking for Book that teaches multiplying multile digits in a single line. (uses -9)

[mamaD]

Back in the late 1960's my father read a book and was fascinated by doing multiple digit multiplication problems in a single line. No adding to get your final answer. It also taught addition, subtraction,and division. He taught me some of this "system" and I am trying to find the author and developer of this system. I was very young and only recall a few details, and am not sure that details are correct.

The author developed this system while incarcerated and I believe it was a German name something like ? Guetenkist.

To check any addition or subtraction you would eliminate everything by 9's and have the same remaining number for the problem and answer.

Thank you for any information that you may be able to provide

 

[Deleted member 4993]

Back in the late 1960's my father read a book and was fascinated by doing multiple digit multiplication problems in a single line. No adding to get your final answer. It also taught addition, subtraction,and division. He taught me some of this "system" and I am trying to find the author and developer of this system. I was very young and only recall a few details, and am not sure that details are correct.

The author developed this system while incarcerated and I believe it was a German name something like ? Guetenkist.

To check any addition or subtraction you would eliminate everything by 9's and have the same remaining number for the problem and answer.

Thank you for any information that you may be able to provide

The method - I think you are talking about - is for checking answer (as opposed to calculating the answer).

https://en.wikipedia.org/wiki/Casting_out_nines

We were taught this method to check our calculations (answers) in the pre-calculator days.