# How to calculate the number of combinations possible

**Introduction:**

Combinations are a fundamental concept in combinatorics, a branch of mathematics that deals with counting and arranging objects. In everyday life, counting possible combinations is quite common, from choosing outfits to selecting lottery numbers. This article will guide you through the process of calculating the number of combinations possible for a given set of items.

**Definition of Combination:**

A combination is a selection of items from a larger set, where the order of the items does not matter. Combinations are often used when we want to find out how many ways we can choose a certain number of items from a larger set without considering their arrangement.

**Formula for Combinations:**

The formula for calculating the number of combinations, denoted as C(n, r) is:

**C(n, r) =** n! / (r! * (n – r)!)

**Here,**

– n represents the total number of items in the set

– r stands for the number of items to be chosen from the set

– ! denotes factorial (e.g., 5! = 5 * 4 * 3 * 2 * 1)

**Step-by-step Guide to Calculate Combinations:**

**1. Understand the problem**: First, determine what needs to be calculated. Identify the total number of items in the set (n) and how many items need to be selected (r).

**2. Find Factorials:** Calculate n!, r!, and (n – r)!. Factorials are found by multiplying all positive integers less than or equal to that number. For example:

**– 5! = 5 * 4 * 3 * 2 * 1**

**– 3! = 3 * 2 * 1**

3. Apply the formula: Substitute n and r values into the formula C(n, r) = n! / (r!*(n – r)!), and compute the result.

Example:

Imagine a deck of cards with 13 distinct cards (n = 13). What are the possible combinations of choosing 5 cards (r = 5)?

**1. n =** 13 and r = 5

**2. Calculate the factorials:**

**– 13! =** 6,227,020,800

**– 5! =** 120

**– (13-5)! =** 8! = 40,320

**3. Substitute n and r into the formula:**

**C(13, 5) =** 13! / (5! * (13-5)!)

**C(13, 5) =** 6,227,020,800 / (120 * 40,320)

**C(13, 5) =** 1,287 combinations

**Conclusion:**

Calculating the number of combinations is a useful skill in various fields ranging from statistics to game theory. By understanding the formula and following this step-by-step guide, you’ll be able to quickly determine the number of possible combinations for any given scenario.