Try this party trick, amaze your friends....

[Xerxes]

This is not as frivolous as the title suggests, but since this subforum seems to have gone into hibernation, try this

 

1. Take any number at all with more than 1 digit and add the digits.

 

2. If the result has more than one digit, add again

 

3. Now subtract this single-digit number from your starting number (not added)

 

4. Add the resulting digits again.

 

5. I bet it will be the number 9

 

Can you see why? Once you do, you will see that the restriction in (1) to more than a single digit is not required.

 

PS If anyone here asks "what is the point of this thread, do I have a question?", the question is already posed, and the "point" is to illustrate an important point in mathematics

[wtf]

Incredible. 2011 called, it wants its post back.

 

http://www.scienceforums.net/topic/54219-even-number-odd-number/

 

See post #6.

Edited January 30, 2016 by wtf

[John Cuthber]

I have the sort of friends who would say "Why didn't you just ask me to reduce the number mod 9" when I got to step 2.

(Well, not all my friends would do that. some would complain that it doesn't work- because they do all their arithmetic in octal, hex or binary.)

Edited January 31, 2016 by John Cuthber

[ajb]

PS If anyone here asks "what is the point of this thread, do I have a question?", the question is already posed, and the "point" is to illustrate an important point in mathematics

The important point is that the difference of any number and the sum of its digits is a multiple of nine? Or is the important point that we have modular arithmetic? Or something else?

[Xerxes]

Incredible. 2011 called, it wants its post back.

And they say that time travel is impossible?

 

Anyway, my apologies - I found it on my hard drive, forgetting why I had put it there (comes from drinking fermented barley juice on a Saturday night).

 

Just ignore me.

 

PS by edit. Actually, in spite of my apology, I am more than a little cross - on 2 occasions I have tried to inject a little life into a moribund subforum, and met with something approaching hostility (I exclude wtf, btw).

 

But don't worry - I shall not try again

Edited January 31, 2016 by Xerxes

[ajb]

But don't worry - I shall not try again

I still think that a blog would be more suitable for the kinds of things you are posting about. You don't really want any feedback or questions answered, rather you want to inform people about things you find interesting. So start a blog, it is easy enough.

[Xerxes]

So, if I am ignorant, confused or merely mad I am welcome to start a new thread in open forum. And not otherwise.

 

This is a strange ethos, and one to which I cannot subscribe. Sorry.

[ajb]

So, if I am ignorant, confused or merely mad I am welcome to start a new thread in open forum. And not otherwise.

We are getting very off topic here, but I think you totally misunderstand.

 

As a discussion forum you should try to post things that allow a discussion to develop. Some of your posts have been about showing us something which you find interesting, this is good, but the way you have posted does not really suggest that you want a two way exchange. So, my suggestion is that blog a lot more on these cool things and you can do that using the scienceforum blogs, if you wish.

 

So in order to rescue this thread...

 

What is the important point you wish to illustrate with your opening post? Do you have a proof of your statement?