Factorial

Rarely Tested

Factorial

## Definition / Concept

The factorial of a positive integer $$n$$ is the product of all positive integers from $1$ to $$n$$.

## Formula

$$n!=n(n-1)(n-2)\cdots2\cdot1$$

Also:

$$0!=1$$

and:

$$n!=n(n-1)!$$

## Usage

- Used extensively in formulas for permutations and combinations.

Question 1

The largest $$n\in \mathbb{N} $$, for which $$7^{n}$$ divides 101!, is :

Question 2

The largest value of n, for which $$40^{n}$$ divides 60! , is

Question 3

In a group of 3 girls and 4 boys, there are two boys $$B_{1}\text{ and }B_{2}$$. The number of ways, in which these girls and boys can stand in a queue such that all the girls stand together, all the boys stand together, but $$B_{1}\text{ and }B_{2}$$ are not adjacent to each other, is :

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