Question 117 of 480
If 6Pr = 6, find the value of 6Pr+1
Correct Answer:
A
Explanation
To solve the problem, we need to understand the notation and the concept of permutations. The notation \( ^nP_r \) represents the number of ways to arrange \( r \) objects from a total of \( n \) distinct objects. The formula for permutations is given by:
\[
^nP_r = \frac{n!}{(n-r)!}
\]
where \( n! \) (n factorial) is the product of all positive integers up to \( n \), and \( (n-r)! \) is the factorial of the difference between \( n \) and \( r \).
### Step 1: Understanding the Given Information
We are given that:
\[
^6P_r = 6
\]
Using the formula for permutations, we can express this as:
\[
^6P_r = \frac{6!}{(6-r)!} = 6
\]
### Step 2: Simplifying the Equation
Now, we can simplify \( 6! \):
\[
6! = 720
\]
So, we can rewrite the equation:
\[
\frac{720}{(6-r)!} = 6
\]
### Step 3: Solving for \( (6-r)! \)
To isolate \( (6-r)! \), we multiply both sides by \( (6-r)! \):
\[
720 = 6 \cdot (6-r)!
\]
Now, divide both sides by 6:
\[
(6-r)! = \frac{720}{6} = 120
\]
### Step 4: Finding \( 6-r \)
Next, we need to find \( 6-r \) such that \( (6-r)! = 120 \). We know that:
\[
5! = 120
\]
Thus, we have:
\[
6 - r = 5
\]
From this, we can solve for \( r \):
\[
r = 6 - 5 = 1
\]
### Step 5: Finding \( ^6P_{r+1} \)
Now that we have \( r = 1 \), we need to find \( ^6P_{r+1} \), which is \( ^6P_2 \):
\[
^6P_2 = \frac{6!}{(6-2)!} = \frac{6!}{4!}
\]
Calculating \( 6! \) and \( 4! \):
\[
6! = 720 \quad \text{and} \quad 4! = 24
\]
Now substituting these values into the permutation formula:
\[
^6P_2 = \frac{720}{24} = 30
\]
### Conclusion
Thus, the value of \( ^6P_{r+1} \) is:
\[
\boxed{30}
\]
### Explanation of Other Options
- **Option B (33)**: This is incorrect because it does not match the calculated value of \( ^6P_2 \).
- **Option C (35)**: This is also incorrect as it does not correspond to any permutation calculation for \( n = 6 \) and \( r = 2 \).
- **Option D (15)**: This is incorrect as well; it does not fit the permutation formula for the given values.
### Revision Summary
- The formula for permutations is \( ^nP_r = \frac{n!}{(n-r)!} \).
- We found \( r \) by solving \( ^6P_r = 6 \) and determined \( r = 1 \).
- We calculated \( ^6P_{r+1} = ^6P_2 = 30 \).
- The correct answer is \( \boxed{30} \).