### You want to know, if you choose three letters from the English Alphabet, how many different sets you will get? What if we restrict that order of the 3 letters is important? That is "abc" is different from "bac." What if we don't care about the order? That is "abc" is the same like "cab", or "cba." The lesson will provide you with the solution to answer these questions, but you have another option. Once this solution starts being developed for you...you might try to continue it till the end by your self by selecting the pen from the MARKER TOOLS menu or simply using your finger if your device allows it and it is practical to do. Having completed the proof or solving the problem you may run the solution and continue the lesson linearly or jumping up or down using the navigability provided by the thumbnails displayed at the left of the screen. Down the page there is a collection of definitions that apply to this lesson. A good student might try to go over them as anticipation for the lesson.

### We start this lesson presenting you a very explicit development of the above cases. After the lesson you will be able to understand the difference between a combination and a permutation. This will in turn enable you to determine probabilities in later lessons. Go get it!

** Lesson's Content **

** Lesson's Glossary **

**Combination: Any arrangement in which order is not important. **

**Factorial! n! represents the product of all the whole numbers from n to 1. n! is the product of all the whole numbers from n down to 1 - used in probability.**

**Permutation: Any arrangement in which order is important. **

**Probability: The possibility of an event to happen. The probability of getting an even number when rolling a 6 sided dice is 50%.**

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