How many ways can they sit in a row?

Proud Pride

In how many ways can 5 people be seated in a straight line?

Factorial NotationWhen we want to multiply all the natural numbers from a particular number down to 1, we can use factorial notation to indicate this operation. The symbol "!" is used to indicate factorial. This notation can save us the trouble of writing a long list of numbers.

For example:6! means 6 x 5 x 4 x 3 x 2 x 1 = 720

4! = 4 x 3 x 2 x 1 = 24

10! = 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 = 3 628 800

1! = 1

By definition 0! = 1

On the calculator ... Press: [MATH]

[<] (Prb) [4] (!)

In how many ways can six students be seated in 8 vacant seats?

Permutations (the "Pick" Formula)

In how many ways can 5 people be seated in a straight line?

In how many ways can six students be seated in 8 vacant seats?

A permutation is an ordered arrangement of objects.

n is the number of objects available to be arranged r is the number of objects that are being arranged.

Examples:

On the calculator ... Press: [MATH]

[<] (Prb) [2] (nPr)

(a) How many “words” of 4 different letters each can be made from the letters A, E, I, O, R, S, T?

(c) In how many of these words do vowels and consonants alternate?

(b) How many of these words begin with a vowel and end with a consonant?

(a) How many numbers of 5 different digits each can be formed from the digits 0, 1, 2, 3, 4, 5, 6?

(b) How many of these numbers are even?

(c) How many of these numbers are divisable by 5?

0, 1, 2, 3, 4, 5, 6?

(a) How many different 4 digit numbers are there in which all the digits are different?

(c) How many of these numbers are divisable by 5?

(b) How many of these numbers are odd?

HOMEWORK

(a) How many 3-digit numbers can be formed if no digit is used more than twice in the same number?

(c) How many of these numbers are divisable by 5?

(b) How many of these numbers are odd?

HOMEWORK

In how many ways can 8 books be arranged on a shelf, if 3 particular books must be together?

HOMEWORK

(a) In how many ways can 4 English books and 3 French books be arranged in a row on a shelf?

(b) In how many of these ways will the French books be together?

HOMEWORK