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digitalmars.D - OT: maths can be so cool...

reply "Regan Heath" <regan netwin.co.nz> writes:
Hi,

This little trick is quite cool. 10 points to the first person to post the  
'reason' why this always works.
   http://digicc.com/fido/
(click the little guy in the bottom right to proceed to next page etc)

Regan
Mar 09 2005
next sibling parent reply brad domain.invalid writes:
Regan Heath wrote:
 Hi,
 
 This little trick is quite cool. 10 points to the first person to post 
 the  'reason' why this always works.
   http://digicc.com/fido/
 (click the little guy in the bottom right to proceed to next page etc)
 
 Regan

Brad
Mar 09 2005
parent reply "Regan Heath" <regan netwin.co.nz> writes:
On Thu, 10 Mar 2005 10:47:24 +1300, <brad domain.invalid> wrote:
 Regan Heath wrote:
 Hi,
  This little trick is quite cool. 10 points to the first person to post  
 the  'reason' why this always works.
   http://digicc.com/fido/
 (click the little guy in the bottom right to proceed to next page etc)
  Regan


No surprises there :) It does ask for a 4 digit number with "lots of different digits" in it. Regan
Mar 09 2005
parent reply pragma <pragma_member pathlink.com> writes:
In article <opsnef8ijt23k2f5 nrage.netwin.co.nz>, Regan Heath says...
On Thu, 10 Mar 2005 10:47:24 +1300, <brad domain.invalid> wrote:
 Regan Heath wrote:
 Doesn't work if you pick a number with the same digits - ie 555

No surprises there :) It does ask for a 4 digit number with "lots of different digits" in it.

Isn't that kind of like asking someone to "draw an 'S', and then a more different 'S'"? - Eric Anderton at yahoo
Mar 09 2005
parent Paul Bonser <misterpib gmail.com> writes:
pragma wrote:
 In article <opsnef8ijt23k2f5 nrage.netwin.co.nz>, Regan Heath says...
 
On Thu, 10 Mar 2005 10:47:24 +1300, <brad domain.invalid> wrote:

Regan Heath wrote:
Doesn't work if you pick a number with the same digits - ie 555

No surprises there :) It does ask for a 4 digit number with "lots of different digits" in it.

Isn't that kind of like asking someone to "draw an 'S', and then a more different 'S'"? - Eric Anderton at yahoo

And maybe a wing...you know..if it's a ... wing-a-ling dragon... And put one of those beefy arms back on for good measure :P -- -PIB -- "C++ also supports the notion of *friends*: cooperative classes that are permitted to see each other's private parts." - Grady Booch
Mar 10 2005
prev sibling next sibling parent reply clayasaurus <clayasaurus gmail.com> writes:
Regan Heath wrote:
 Hi,
 
 This little trick is quite cool. 10 points to the first person to post 
 the  'reason' why this always works.
   http://digicc.com/fido/
 (click the little guy in the bottom right to proceed to next page etc)
 
 Regan

would be better if the flash wasn't as annoying :-/ hard to read with all those distractions in the background and constant sound effects
Mar 09 2005
parent "Regan Heath" <regan netwin.co.nz> writes:
On Wed, 09 Mar 2005 18:28:29 -0500, clayasaurus <clayasaurus gmail.com>  
wrote:
 Regan Heath wrote:
 Hi,
  This little trick is quite cool. 10 points to the first person to post  
 the  'reason' why this always works.
   http://digicc.com/fido/
 (click the little guy in the bottom right to proceed to next page etc)
  Regan

would be better if the flash wasn't as annoying :-/ hard to read with all those distractions in the background and constant sound effects

Yeah.. Don't blame me, I didn't write it :) Regan
Mar 09 2005
prev sibling next sibling parent zwang <nehzgnaw gmail.com> writes:
Regan Heath wrote:
 Hi,
 
 This little trick is quite cool. 10 points to the first person to post 
 the  'reason' why this always works.
   http://digicc.com/fido/
 (click the little guy in the bottom right to proceed to next page etc)
 
 Regan

Here's my solution in D :) int marked(int[] num){ assert(num.length); int j; foreach(int i; num){ assert(1<=i && i<=9); j+=i; } return 9-j%9; }
Mar 09 2005
prev sibling parent reply "Unknown W. Brackets" <unknown simplemachines.org> writes:
I remember these from... like 10 years ago or more.  It's pretty simple. 
  First I'll walk through it:

Let's say you're given 1234 and 3412. You subtract:

3412 - 1234 = 2178

So the possibles are 1, 2, 7, 8.  Let's say you picked "2".... so 1, 7, 
and 8.  And it gets 2.  Amazing, you think?

Watch me with some other numbers:

4321 - 1234 = 3087
4231 - 1234 = 2997
4123 - 1234 = 2889
4132 - 1234 = 2898

Okay, that's enough of a sample.  Let's add now, a step it skips for you:

2 + 1 + 7 + 8 = 18
3 + 0 + 8 + 7 = 18
2 + 9 + 9 + 7 = 27
2 + 8 + 8 + 9 = 27
2 + 8 + 9 + 8 = 27

The real trick is, people think it knows your number.  It doesn't... it 
just knows the digits HAVE to add up to a multiple of nine, because 
you're subtracting digits from themselves (even in a funky order.)

The only problem is if you circle a NINE or a ZERO, you can't tell the 
difference.  That's why you're not allowed to circle zeros, which makes 
it certain that you're only circling 9's in that case.

I knew how this worked before I even learned real algebra ;).  Do I get 
10 points now :P?

-[Unknown]


 Hi,
 
 This little trick is quite cool. 10 points to the first person to post 
 the  'reason' why this always works.
   http://digicc.com/fido/
 (click the little guy in the bottom right to proceed to next page etc)
 
 Regan

Mar 09 2005
parent reply "Regan Heath" <regan netwin.co.nz> writes:
On Wed, 09 Mar 2005 23:03:46 -0800, Unknown W. Brackets  
<unknown simplemachines.org> wrote:
 I knew how this worked before I even learned real algebra ;).  Do I get  
 10 points now :P?

Yes. Regan
Mar 13 2005
parent "Unknown W. Brackets" <unknown simplemachines.org> writes:
Yea!

Heh... I probably didn't even explain it that well.  But, it is a very 
interesting concept that the numbers could be so predictable.  I spent 
hours thinking about it back when I first figured it out.

-[Unknown]


 On Wed, 09 Mar 2005 23:03:46 -0800, Unknown W. Brackets  
 <unknown simplemachines.org> wrote:
 
 I knew how this worked before I even learned real algebra ;).  Do I 
 get  10 points now :P?

Yes. Regan

Mar 13 2005