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
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