Question

Evaluate the expression. \({ }_{30} P_2\)

Short answer

The evaluated expression \({ }_{30} P_2\) is 870.

Step-by-step solution

Understand the permutation formula

The permutation formula is P(n, r) = \frac{n!}{(n - r)!}. In the given problem, n is 30 and r is 2. ! represents factorial, which is the product of an integer and all the integers below it. For example, 4! is 4 x 3 x 2 x 1 = 24.

Apply the permutation formula

Substitute 30 for n and 2 for r in the formula to get \({ }_{30} P_2 = \frac{30!}{(30 - 2)!} = \frac{30!}{28!}\).

Simplify the expression

We can simplify this by only working out the first few terms of the factorial that are not cancelled out. That is, \({ }_{30} P_2 = \frac{30!}{28!} = \frac{30 \times 29 \times 28!}{28!} = 30 \times 29 = 870\).

Key concepts

Factorial

A factorial, often represented by an exclamation point (!), is a basic concept in mathematics. It involves multiplying a positive integer by all the positive integers less than itself. For example, if you see 4!, this indicates 4 factorial, which means \(4 \times 3 \times 2 \times 1 = 24\). Factorials are crucial as they form the foundation for more complex calculations in combinatorics and probability. They essentially help to arrange or organize items in different sequences or orders.

• When you see \(n!\), read it as "n factorial".
• 0! is conventionally equal to 1. This is an important rule in factorial calculations.

Factorials grow rapidly, making them suitable for calculations that require large numbers, such as permutations and combinations. Understanding how to compute factorials is necessary for evaluating expressions in algebra and calculus.

Permutation Formula

The permutation formula is used in mathematics to determine the number of ways to arrange a subset of items from a larger set. When you apply this formula, you are essentially finding the different sequences possible when a specific number of items is selected from a larger pool. The formula is expressed as:\(P(n, r) = \frac{n!}{(n-r)!}\)

• \(n\) represents the total number of items.
• \(r\) is the number of selected items.

This formula comes in handy when order matters. For instance, if you need to find out how many ways you can arrange 2 trophies on a shelf out of 30, you use \(P(30, 2) = \frac{30!}{28!} = 30 \times 29 = 870\).The permutation formula is important in tasks where sequence or arrangement is critical, such as seating arrangements, passwords, etc.

Combinatorics

Combinatorics is the branch of mathematics that deals with counting, arrangement, and combination of objects. It helps to solve problems related to how things can be counted or arranged without necessarily doing it by hand. Two main types in combinatorics are permutations and combinations.

• Permutations: Arrangements of items where order does matter. Used when organizing items sequentially.
• Combinations: Selections of items where order doesn't matter. Used when you're forming groups or sets.

Combinatorics applies to several real-world scenarios, from optimizing schedules to creating secure cryptographic systems. Knowledge in combinatorics allows us to evaluate probabilities and make informed decisions in everyday life.