[Kees]

If you want to know the number of my post count when i write this you can always compute it using random numbers.
Pick any number consisting of three different digits.
Create a second number by reversing the digits in the first number.
Subtract the smaller number from the larger one.
Thus you created a third three digit number (add leading zeroes if needed).
Create a fourth number by reversing the digits in this third number.
Add these last two numbers.

 

[aluren]

interesting... just wasted 5 min of my time, but interesting nonetheless...

 

[Febs]

Clever.

 

[tennisets]

Huh, interesting. Any math guys want to explain why this works? I am but a lowly engineer.

 

[Fitz]

Kees makes Fitz brain hurt with the staggering implications of this discovery.

 

[adanac061]

Well Im no math guy, but from a cursory examination it seems the middle number cancels itself out in the first calculation.

for example 321-123. What the two number have in common is 20,
and 20- 20 =0

also
765- 567 have 60 in common, and 60-60 =0

so really 321-123 is 301- 103 which equals 198

and 765 - 567 is really 705 -507 which equals 198

Now here's the clever part. ...

Because the middle digit is really always 0, And the smaller number is always subtracted from the larger number, this limits your choice of "random numbers" in real life to the following combinations after duplicates are eliminated. >>

You really only get to choose the following combinations :

102 reversed is 201
103 reversed is 301
104 " 401
105 " 501
106 " 601
107 701
108 801
109 901
203 302
204 402
205 502
206 602
207 702
208 802
209 902
304 403
305 503
306 603
307 703
308 803
309 903
405 504
406 604
407 704
408 804
409 904
506 605
507 705
508 805
509 905
607 706
608 806
609 906
708 807
709 907
809 908

Every one of those sums always equals one of the following numbers :

198
297
396
495
594
693
792
891

The last part of the trick is to add the last two numbers together.
The middle digit is always 9 (see above) and that means 90 + 90 =180

If we decide to just add the 180 after the last calculation it becomes
alot clearer how this works.

The real sums look like :
108 +801 = 909 + the 180 = 1089*
207 + 702 = 909 + the 180 = 1089*
306 + 603 = 909 + the 180 = 1089*
405+ 504 = 909 + the 180 = 1089*
504+ 405 = 909 + the 180 = 1089*
603+ 306 = 909 + the 180 = 1089*
702+ 207 = 909 + the 180 = 1089*
801 + 108 = 909 + the 180 = 1089*

what do you think???

 

[Fitz]

I think you have too much free time.

 

[Mrvile]

I think you are a math guy. Don't lie.

 

[Fitz]

Stop stalking me.

 

[Mrvile]

Quote:

Originally Posted by Fitz /img/forum/go_quote.gif Stop stalking me.

I was actually referring to adanac. Don't expect to get all my attention. You get a lot of it, but not all of it.

 

[Kees]

The proof is quite simple actually:
ABC is a number with three different digits.
A<>B, A<>C and B<>C
CBA is the number with inverted digits.
That means A is either bigger or smaller than C.
We can assume bigger, for the other case if A is smaller, would result in an identical proof with the two numbers switched.
This means ABC is the larger number.

A B C
C B A
_______________________________________________ subtract

A>C so I have to “borrow” 10 from B. Then B is bigger then B-1 so
I also have to “borrow” 10 from A.

(A-1-C) (B-1+10-B) (C+10-A)
(C+10-A) (B-1+10-B) (A-1-C) inverse

_______________________________________________ add
(A-1-C+C+10-A) (B-1+10-B+B-1+10-B) (C+10-A+A-1-C)

9 8+10 9 carry over
10 8 9