Math Problem Statement

If nP4 = 12 × nP2, find n.

Solution

To solve the given problem, we use the formula for permutations:

nPr=n!(nr)!^nP_r = \frac{n!}{(n-r)!}

The given equation is:

nP4=12nP2^nP_4 = 12 \cdot ^nP_2

Substituting the permutation formula:

n!(n4)!=12n!(n2)!\frac{n!}{(n-4)!} = 12 \cdot \frac{n!}{(n-2)!}

Simplify by canceling n!n! on both sides:

1(n4)!=121(n2)(n3)(n4)!\frac{1}{(n-4)!} = 12 \cdot \frac{1}{(n-2)(n-3)(n-4)!}

Simplify further by canceling (n4)!(n-4)!:

1=12(n2)(n3)1 = \frac{12}{(n-2)(n-3)}

Multiply through by (n2)(n3)(n-2)(n-3):

(n2)(n3)=12(n-2)(n-3) = 12

Expand and simplify:

n25n+6=12n^2 - 5n + 6 = 12

n25n6=0n^2 - 5n - 6 = 0

Factorize:

(n6)(n+1)=0(n-6)(n+1) = 0

So:

n=6orn=1n = 6 \quad \text{or} \quad n = -1

Since nn must be a positive integer, n=6n = 6.

Final Answer:

n=6n = 6

Would you like a detailed breakdown of any step?

Here are 5 related questions for deeper exploration:

  1. What is the difference between permutations and combinations?
  2. How do factorials simplify expressions involving permutations?
  3. Can this method be used to solve any permutation-based equation?
  4. What happens if the values of rr in the permutations differ significantly?
  5. How do negative results for nn affect practical problems?

Tip: Always ensure that factorial terms in permutations are simplified to avoid overly complex equations.

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Math Problem Analysis

Mathematical Concepts

Permutations
Factorials
Algebra

Formulas

^nP_r = n! / (n - r)!

Theorems

Basic Permutation Formula

Suitable Grade Level

Grades 10-12