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**Nfe789****Member**- Registered: 2010-12-10
- Posts: 5

Hello there, names is N. Emi. I'm a 3rd class petty officer USN.

I have a question about permutation and combination, working with a two part lock, first part is a "combination lock" choosing 3 numbers 1-99, second is a key pad that consist of 9 numbers, and here the password can be 121234524 but it cannot be 122113441, you cannot follow a number (ie 2) with the same number (2), but they can repeat. Were locked out of a space onboard... And were trying to crack it... Rediculous right? My chiefs crazy... He wants it open and he said you're a ctt figure it out. Lol and we get the gist there's well over 100 million possiblities... Help? Lol trying to keep it on the DL

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**Nfe789****Member**- Registered: 2010-12-10
- Posts: 5

We started to try with the basic 0-0-0 / 0-0-0-0-0-0-0-0-0 then 0-0-0 / 0-0-0-0-0-0-0-0-1 lol realizing we could not repeat numbers one after another. So we really do know where to start. But our chief wants some kinda proof to say this is rediculous.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi Nfe789;

Welcome to the forum!

choosing 3 numbers 1-99,

Just a minor problem you say that the first part of the lock is a combination lock with 3 numbers 1 - 99 but you show 0-0-0 / 0-0-0-0-0-0-0-0-0 as your first try. Should it not be 1-1-1 / 0-0-0-0-0-0-0-0-0?

You can tell your chief ( with respect of course ) that a trial and error approach is useless there are

(99^3) * 430 467 210 ( this underlined number is experimental ) = 417 681 903 395 790 possible codes. If you were to enter them at 1 per second it would take you 6 622 303 years to open it.

Rather than trying this brute force approach. If you know who set the password, in this case the numbers, try to crack it based on what you know about the man. He may have used his birthdate, lucky numbers, a badge number, his age, they may all be part of the code.

Remember, humans use passwords ( numbers or letters ) that are easy to remember. Do not rule out possibilities like 123 123 123 or 123 456 789 etc.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**Nfe789****Member**- Registered: 2010-12-10
- Posts: 5

The combo lock is digital too 00-99 sorry for the error, however the password are purposly generated in no relation to personal. Lol ironicly my chief made the password.

Everysecond I wish, there is a 3 minute wait time between incorrect entries

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi Nfe789;

That is even better, then there are

100^3 * 430 467 210 ( this underlined number is experimental ) = 430 467 210 000 000 codes. It will take approximately 1 228 502 311 years to crack it. Quite hopeless to stumble on it by trial and error, or a systematic try them all approach.

however the password are purposly generated in no relation to personal

Bravo! Glad to see the navy is doing a better job than the corporate sector!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**Nfe789****Member**- Registered: 2010-12-10
- Posts: 5

So lol how many possiblities are there concerning the 3 number combination lock and the digital key pad that can repeat numbers but not repeat one after the other?

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

100^3 = 1 000 000 for the 3 number combination lock

430 467 210 for the numeric keypad.

The two together is 100^3 * 430 467 210 = 430 467 210 000 000 codes.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

The numeric keypad only has 9 numbers on it, so the amount of combinations to try is only 150,994,944.

I've just saved you a few hundred million years!

Why did the vector cross the road?

It wanted to be normal.

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**soroban****Member**- Registered: 2007-03-09
- Posts: 452

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi all;

soroban wrote:

I agree with bobbym.

I often agree with him too.

mathsyperson wrote:

The numeric keypad only has 9 numbers on it, so the amount of combinations to try is only 150,994,944.

My calculation and soroban's is based on a 10 digit keypad. But the problem reads.

Nfe789 wrote:

second is a key pad that consist of 9 numbers,

Mathsyperson who insists on reading questions thoroughly, is then quite correct.

Marcus Penn wrote:

Assumption is the mother of all foul ups

But since the OP had a typo on 1-99 when he meant 0 - 99, and due to the fact that I have never seen a nine digit numeric keypad I assumed he meant a ten digit keypad.

So Nfe789, which is it, a nine digit ( 1 - 9 ) or a 10 digit ( 0 - 9 )? Millions of years are at stake!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,167

hi Nfe789

Because of the 'special relationship across the pond' the Queen says it's ok for me to chip in here. What about the actual engineering aspects of this problem?

(i) Can you just, in the words of Michael Caine, "blow the bloody doors off"

(ii) Suppose I tried a combination lock number and got it right. Would there be any clue that I'd done that bit even though the other bit is still wrong? Because that reduces the problem loads and loads.

(iii) Do you have any safe breakers on board?

Bob

*Last edited by bob bundy (2010-12-11 00:54:07)*

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**Nfe789****Member**- Registered: 2010-12-10
- Posts: 5

I'm one of the cryptos on board... I am the safe breaker out to sea

and it's a 0-99. Combo lock and 0-9 key pad but the pass word is 9 numbers

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

That is what I figured. What will you do?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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