
New Member
Combinations/Permutations where only certain elements in series can vary
Hi all,
I am sorry if this is posted the wrong subforum, but my math knowledge is limited and so I am unsure where else to post.
I am wondering how to calculate the number of possible versions of a series of characters, where only some characters in the series can vary.
5NMB RTTM 8L60 9P7U AJQW 9889
5 
N 
M 
B 
R 
T 
T 
M 
8 
L 
6 
0 
9 
P 
7 
U 
A 
J 
Q 
W 
9 
8 
8 
9 




L 


N 


G 
O 


4 


3 

V 

B 
B 

How many different combinations are possible where only bold characters can vary and they can vary only with the character directly beneath them in the table? Is there a formula for this?
Therefore, the following are possible (characters in red are variations on the original series):
5NMB LTTM 8L60 9P4U AJQW 9889
5NMB RTTM 8L60 9P7U AJQW 9BB9
5NMB LTTN 8LGO 9P4U A3QV 9889
But the following is NOT:
5NMB NTTO 8L60 9P7U ABQB 93V9
I hope this makes sense, and I hope it is ok to post here. I am new to the forum so forgive me if my posting etiquette or anything is offpoint.
I look forward to your responses.

Senior Member
If I understand the problem, you have a sequence of characters. At specific spots in the sequence, a character may be replaced by one other character.
You have 9 spots where an alternative is permitted.
So the number of possible different sequences is [tex]2^9 = 512.[/tex]
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