The formula for a combination of choosing

_{n}C_{r} = | n! |

r!(n - r)! |

where n is the number of items and r is the unique arrangements.

_{5}C_{0} = | 5! |

0!(5 - 0)! |

Remember from our factorial lesson that n! = n * (n - 1) * (n - 2) * .... * 2 * 1

n! = 5!

5! = 5 x 4 x 3 x 2 x 1

5! = 120

(n - r)! = (5 - 0)!

(5 - 0)! = 5!

5! = 5 x 4 x 3 x 2 x 1

5! = 120

r! = 0!

0! =

0! = 1

_{5}C_{0} = | 120 |

1 x 120 |

_{5}C_{0} = | 120 |

120 |