Question 1
In how many ways can 7 guests be seated in a circular arrangement? (Consider rotations as the same)
Step-by-Step Solution:
Concept: Circular permutation formula = (n-1)! when clockwise and anticlockwise are considered different, and rotations are considered the same.
Why (n-1)! and not n!?
In a circle, there's no fixed starting point. Rotations of the same arrangement are identical.
Analysis:
- If arranged in a line: 7! = 5040 ways
- But in a circle: we fix one person's position as reference
- Remaining 6 people can be arranged in 6! ways
Calculation:
Circular arrangements = (7-1)! = 6! = 720
Intuition: Fix one person at a position (say 12 o'clock). Now arrange the remaining 6 people in the 6 positions clockwise.
Formula Summary:
- Linear permutation: n!
- Circular permutation (rotations same): (n-1)!
- Circular permutation (reflections also same): (n-1)!/2
Common Error: Don't use n! for circular arrangements - this counts rotations as different arrangements.
Concept: Circular permutation formula = (n-1)! when clockwise and anticlockwise are considered different, and rotations are considered the same.
Why (n-1)! and not n!?
In a circle, there's no fixed starting point. Rotations of the same arrangement are identical.
Analysis:
- If arranged in a line: 7! = 5040 ways
- But in a circle: we fix one person's position as reference
- Remaining 6 people can be arranged in 6! ways
Calculation:
Circular arrangements = (7-1)! = 6! = 720
Intuition: Fix one person at a position (say 12 o'clock). Now arrange the remaining 6 people in the 6 positions clockwise.
Formula Summary:
- Linear permutation: n!
- Circular permutation (rotations same): (n-1)!
- Circular permutation (reflections also same): (n-1)!/2
Common Error: Don't use n! for circular arrangements - this counts rotations as different arrangements.