Math Problem Statement

Evaluate the expression. StartFraction 11 Upper P 2 Over 2 exclamation mark EndFraction minus 11 Upper C 2

Solution

To evaluate the expression:

11P22!11C2\frac{11P2}{2!} - 11C2

Let's break it down into two parts:

1. Permutations ( 11P211P2 ):

The permutation formula for nPrnP r is:

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

For 11P211P2, we have:

11P2=11!(112)!=11!9!11P2 = \frac{11!}{(11-2)!} = \frac{11!}{9!}

Now simplify 11!11! and 9!9!:

11!=11×10×9!11! = 11 \times 10 \times 9!

So,

11P2=11×10×9!9!=11×10=11011P2 = \frac{11 \times 10 \times 9!}{9!} = 11 \times 10 = 110

2. Factorial of 2 ( 2!2! ):

2!=2×1=22! = 2 \times 1 = 2

Now, compute the first part of the expression:

11P22!=1102=55\frac{11P2}{2!} = \frac{110}{2} = 55

3. Combinations ( 11C211C2 ):

The combination formula for nCrnC r is:

nCr=n!r!(nr)!nC r = \frac{n!}{r!(n-r)!}

For 11C211C2, we have:

11C2=11!2!(112)!=11!2!9!11C2 = \frac{11!}{2!(11-2)!} = \frac{11!}{2!9!}

Using 11!=11×10×9!11! = 11 \times 10 \times 9! and 9!9! cancels out:

11C2=11×102!=1102=5511C2 = \frac{11 \times 10}{2!} = \frac{110}{2} = 55

Final Calculation:

Now substitute these values back into the original expression:

11P22!11C2=5555=0\frac{11P2}{2!} - 11C2 = 55 - 55 = 0

Thus, the value of the expression is:

0\boxed{0}


Would you like further details or have any questions? Here's a list of related topics you might find interesting:

  1. How does the permutation formula change with different values of rr?
  2. The difference between permutations and combinations in real-life examples.
  3. How do factorials behave as the numbers increase?
  4. Application of combinations and permutations in probability theory.
  5. How do you derive the combination formula?

Tip: Always be cautious when interpreting permutations and combinations — permutations consider order, while combinations do not.

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Math Problem Analysis

Mathematical Concepts

Permutations
Combinations
Factorials

Formulas

nP r = n! / (n-r)!
nC r = n! / (r!(n-r)!)
n! = n × (n-1) × (n-2) × ... × 1

Theorems

Permutations and combinations

Suitable Grade Level

Grades 10-12