rmn_tech
Member
A friend has constructed a simple electronic lock and I was trying to explain that it is not as secure as he thinks. It is a 4 digit entry code (digits 0 - 9) he thinks that there are 10,000 combinations (0000 - 9999)
However he has not taken into account that no digit can be used more than once in the unlock code, e.g. 1757 (2 x 7's) etc
Also the code can be entered in any order, e.g 1234 (can be entered as 4321, 2314, 3214, etc.)
What I am trying to work out is how many individual unique codes are available for use.
Recap
4 Digit code
digits from 0 to 9
no digit can be repeated in the code
no code can contain the same digits in different orders.
I don't expect anyone to work this out for me. I would however appreciate it if one of you good people could give me a formula or some clues to help me work this out.
Thanks in advance.
Rick.
However he has not taken into account that no digit can be used more than once in the unlock code, e.g. 1757 (2 x 7's) etc
Also the code can be entered in any order, e.g 1234 (can be entered as 4321, 2314, 3214, etc.)
What I am trying to work out is how many individual unique codes are available for use.
Recap
4 Digit code
digits from 0 to 9
no digit can be repeated in the code
no code can contain the same digits in different orders.
I don't expect anyone to work this out for me. I would however appreciate it if one of you good people could give me a formula or some clues to help me work this out.
Thanks in advance.
Rick.