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Factorial) – Texas Instruments TI-73 EXPLORER User Manual

Page 58

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52

Chapter 2: Math Operations

7302ENG.DOC CH2 Math Operations, English Julie Hewlett Revised: 07/29/98 11:58 AM Printed: 05/19/99 8:58

AM Page 52 of 32

From a group of 4 items (ABCD), how many ways can you

select 2 of the items if the order does not matter?
Find 4

nCr

2.

:

4

1 " "

4

2

b

ABCD

AB

AC

AD

BA

BC

BD

CA

CB

CD

DA

DB

DC

!

! 1

"

"

5

5

Returns the factorial of value. value can be an integer or list of

integers between 0 and 69. By definition, 0! = 1.
Factorials are similar to permutations because the order

DOES matter. You can think of 4! as the total number of ways

that 4 items can be arranged.

value

!

Find 4!

:

4

1 " "

5

b

ABCD

ABCD

ABDC

ACBD

ACDB

ADBC

ADCB

BACD

BADC

BCAD

BCDA

BDCA

BDAC

CABD

CADB

CBAD

CBDA

CDAB

CDBA

DABC

DACB

DBAC

DBCA

DCAB

DCBA

³

³

4! = 4

Q

3

Q

2

Q

1

AB and BA count

as only one

combination.

4!

4 items taken

2 at a time

combinations of

24 possible arrangements