MHB Number of ways to arrange letters

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The exercise involves calculating the number of arrangements for 5 letters A, 3 letters B, and 4 letters C. The correct formula for this calculation is given as (12!)/(5! * 3! * 4!). Participants confirm the initial calculation is accurate and explore alternative methods to derive the same result. There is some frustration expressed regarding the lack of instructional support from the textbook or instructor in providing methods for solving such problems. Overall, the discussion emphasizes the correct approach to combinatorial arrangements.
evinda
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Hey again! :)

I am given this exercise:
With how many ways can we arrange $5$ letters $A$, $3$ letters $B$ and $4$ letters $C$?

I thought that it is :

$$\frac{(5+3+4)!}{5! \cdot 3! \cdot 4!}=\frac{12!}{5! \cdot 3! \cdot 4!}$$

Could you tell me if it is right? (Blush)
 
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evinda said:
Hey again! :)

I am given this exercise:
With how many ways can we arrange $5$ letters $A$, $3$ letters $B$ and $4$ letters $C$?

I thought that it is :

$$\frac{(5+3+4)!}{5! \cdot 3! \cdot 4!}=\frac{12!}{5! \cdot 3! \cdot 4!}$$

Could you tell me if it is right? (Blush)

Yep.
It is right! (Mmm)
 
I like Serena said:
Yep.
It is right! (Mmm)

Nice,thank you! :)
 
I would have said that the answer is:
\[(\begin{matrix}12\\5\end{matrix})(\begin{matrix}7\\4\end{matrix})=(\begin{matrix}12\\4\end{matrix})(\begin{matrix}8\\5\end{matrix})=
(\begin{matrix}12\\3\end{matrix})(\begin{matrix}9\\4\end{matrix}) etc.=\frac{12!}{3!\cdot4!\cdot5!}\]

I don't understand the purpose of Evinda's instructor or textbook asking for so many answers to be computed only without also supplying methods or proofs.
 

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