Question 1
A word has 7 letters: 2 as, 2 bs, 3 cs. How many distinct ways can these letters be arranged?
Step-by-Step Solution:
Concept: Permutations with identical objects. When objects of the same type are indistinguishable, we divide by the factorial of each type's count.
Formula:
$$\frac{n!}{n_1! \cdot n_2! \cdot ... \cdot n_k!}$$
where $n$ is total objects and $n_i$ is the count of type $i$.
Given Data:
- Total objects: 7
- Distribution: Type 1: 2, Type 2: 2, Type 3: 3
Step 1 - Total arrangements if all were distinct:
7! = 5040
Step 2 - Account for identical objects:
7! = 5040 / 2! = 2 / 2! = 2 / 3! = 6
Final Calculation:
= 210
Key Principle: Each group of identical objects overcounts by a factor of (count)!. Division corrects this.
Verification: The result is an integer and less than 7! = 5040.
Concept: Permutations with identical objects. When objects of the same type are indistinguishable, we divide by the factorial of each type's count.
Formula:
$$\frac{n!}{n_1! \cdot n_2! \cdot ... \cdot n_k!}$$
where $n$ is total objects and $n_i$ is the count of type $i$.
Given Data:
- Total objects: 7
- Distribution: Type 1: 2, Type 2: 2, Type 3: 3
Step 1 - Total arrangements if all were distinct:
7! = 5040
Step 2 - Account for identical objects:
7! = 5040 / 2! = 2 / 2! = 2 / 3! = 6
Final Calculation:
= 210
Key Principle: Each group of identical objects overcounts by a factor of (count)!. Division corrects this.
Verification: The result is an integer and less than 7! = 5040.