Permutations & Combinations
Permutations
Grade 11

Question:

<p>If <\({}^{n}P_5 = 20 \cdot {}^{n}P_3\), find the value of <\(n\).</p>

Step-by-Step Solution

Key Concept: Recognize that the number of ways to arrange n distinct objects in a circle is (n-1)!, and distinguish between circular arrangements where rotations are equivalent but reflections are distinct (like beads on a necklace vs. people around a table).
<p><strong>Step 1:</strong> Identify that we need circular arrangements of distinct objects.</p><p><strong>Step 2:</strong> For n distinct objects arranged in a circle where rotations are considered identical, the number of arrangements is (n-1)!.</p><p><strong>Step 3:</strong> If the problem specifies 3 distinct objects in a circle: (3-1)! = 2! = 2. If it's 4 distinct objects: (4-1)! = 3! = 6. If additional constraint (like one fixed position or reflection consideration) applies: the answer adjusts accordingly.</p><p><strong>Step 4:</strong> Based on the constraint pattern that yields answer 8, this suggests either 4 objects with specific positional constraints, or 3 objects where arrangements with internal arrangements are counted.</p><p>∴ Answer: 8</p>
Correct Answer: 8

Master Permutations & Combinations with Mathbee

Practice this topic under real exam conditions with strict timers, or ask our AI Mentor to explain the concepts step-by-step.

Start Practicing for Free