Permutations and Combinations

**Fundamental Principle of Counting:**If an event occurs in*m*different ways, following which another event occurs in*n*different ways, then the total number of occurrence of the events in the given order is*m*×*n*. This is called the fundamental principle of counting.

**Example:**

Find the number of 5-letter words, with or without meaning, which can be formed out of the letters of the word MATHS, where the repetition of digits is not allowed.

There are as many words as there are ways of filling 5 vacant places by the 5 letters.

The first place can…

**Solution:**There are as many words as there are ways of filling 5 vacant places by the 5 letters.

The first place can…

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