



 
Hi Rob. It depends on whether duplicates are allowed. For example, is Y, X, LT, X allowed? It also depends on whether order is important. Is Y, X, LT, RT different from RT, Y, X, LT? Assuming the answers to both question are Yes, you have 6 choices for each of the four positions, so the number of possibilities is 6 x 6 x 6 x 6. If duplicates are not allowed, then you have 6 choices for the first symbol, 5 for the next, etc. So the number of possibilities is 6 x 5 x 4 x 3. If order is not important, you have to weed out duplicates. The number of duplicates is the number of ways of arranging 4 things: 4 x 3 x 2 x 1 . So you would divide the number of possibilities by 24. Cheers,  


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