I am having a great deal of trouble with one question which I have not been able to solve. I am having trouble picturing the problem. I was wondering if anyone could help me by showing me the steps to solving the problem and with the solution.
Three molecules of type A, three of type B, three of type C, and three of type D are to be linked together to form a chain molecule. One such chain molecule is ABCDABCDABCD,and another is BCDDAAABDBCC.
(a) How many such chain molecules are there? [Hint: If the three A's were distinguishable from one another -- A1, A2, A3 -- and the B's, C's, and D's were also, how many molecules would there be? How is this number reduced when the subscripts are removed from the A's?
(A1 means A subscript 1, same for A2 and A3)
The final answer isn't important to me, but the steps are. I really want to understand this problem. Please if anyone can help me I would greatly appreciate it. Thank you in advance!