PermutationsObjectives: Solve problems involving linear permutations of distinct or indistinguishable objects. Solve problems involving circular

permutations.

Standards: 2.7.8A Determine the number of permutations for an event.

A permutation is an arrangement of objects in a specific order.

When objects are arranged in row, the permutation is called a linear permutation.

You can use factorial notation to abbreviate this product:

4! = 4 x 3 x 2 x 1 = 24. If n is a positive integer, then n factorial,

written n!, is defined as follows:n! = n x (n-1) x (n-2) x . . . x 2 x 1.

Note that the value of 0! = 1.

I. Permutations of n Objects - the number ofpermutations of n objects is given by n!

{factorial button – go to Math to PRB to # 4}

Ex 1. In 12-tone music, each of the 12 notes in an octave must be used exactly once before any are repeated. A set of 12 tones is called a tone row. How many different tone rows are possible?

Ex 2. How many different ways can the letters in the word objects be arranged?

12! = 479,001, 600

7! = 5040

II. Permutations of n Objects Taken r at a Time – the number of permutations of n

objects taken r at a time, denoted by P(n, r), is given by P(n, r) = nPr =__n!_, where r < n.

(n–r)!

Ex 1. Find the number of ways to listen to 5 different CDs from a selection of 15 CDs.

Ex 2. Find the number of ways to listen to 4 CDs from a selection of 8 CDs.

Ex 3. Find the number of ways to listen to 3 different CDs from a selection of 5 CDs.

15 P 5 = 360, 360

8 P 4 = 1680

5 P 3 = 60

III. Permutations with Identical Objects – the number of distinct permutations of

n objects with r identical objects is given by n!/r! where 1 < r < n. The

number of distinct permutations of n objects with r1 identical objects, r2 identical objects of another kind, r3

identical objects of another kind, . . . , and rk identical objects of another kind

is given by_______n! _ .

r1 ! * r2 ! * r3 ! . . . rk !

Ex 1. Anna is planting 11 colored flowers in a line. In how many ways can she plant 4 red flowers,

5 yellow flowers, and 2 purple flowers?

Ex 2. In how many ways can Anna plant 11 colored flowers if 5 are white and the remaining ones are red?

11!__ (5! * 6!)

= 462

Ex 3. Frank is organizing sports equipment for the physical education room. He has 15 balls that he must place in a line.

In how many ways can he line up 6 footballs, 2 soccer balls, 4 kickballs, and 3 basketballs?

Ex. 4 BETWEEN

____15!______(6! * 2! * 4! * 3!)

= 6,306,300

7!3! = 840

III. Circular Permutations - If n distinct objects are arranged around a circle, then

there are (n – 1)! Circular permutations of the n objects.

Ex 2. In how many ways can seats be chosen for 12 couples on a Ferris wheel that has 12 double seats?

Ex 3. In how many different ways can 17 students attending a seminar be arranged in a circular seating pattern?

(12 – 1)! = 11! = 39, 916, 800

(17 – 1)! = 16! = 2.09 X 1013

Writing Activities

REVIEW OF PERMUTATIONS