## Introduction to Permutation and Combination

Permutation and combination questions involve finding the number of possible ways for a given scenario.

For example, the number of ways of selecting 3 people out of a total of 50 people is an example of a combination question (order does not matter).

The number of ways of arranging 5 books side by side is an example of a permutation question (order matters).

Watch the video below for a better understanding between permutation and combination

## Addition and Multiplication Rule

We add all the number of ways together to get the total number of ways if these ways cannot occur simultaneously.

We multiply the number of ways to get total number of ways if these ways must occur simultaneously.

# Formulae for permutation and combination

- Number of ways to arrange n objects = n!
- Number of ways to arrange n objects with r of them being repeated units: n!/r!
- Number of ways to arrange n objects in a circle = (n-1)!
- Number of ways to permutate r objects from a set of n objects = nPr
- Number of ways to choose r objects from a set of n objects without permutation = nCr

## How to approach H2 A Level Math Statistics Questions

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