CFALA
Review:
Tips
for
using
the
TI
calculator
2/9/2015
By
David
Cary
18
Factorial,
Combinations,
and
Permutations
•
N
Factorial
(N!)
is
when
you
multiply
N
x
(N
‐
1)
x
(N
‐
2)
x
…
x
2
x
1
=
N!
•
There
is
a
built
in
function
in
your
calculator
to
do
this:
[2
nd
][x]
=
[x!],
To
get
5!:
5
[2
nd
][x!]
=
120
•
This
can
be
useful
for
combination
calculations:
To
select
a
subset
of
3
items
out
of
5:
5
C
3
=
5!
/
((5
‐
3!)(3!))
=
10
Your
TI
has
a
built
in
function
for
this:
[2
nd
][+]
=
[
n
C
r
]
5
C
3
=
5
[2
nd
][
n
C
r
]
3
[=]
10
CFA Society Los Angeles
35
Factorial,
Combinations,
and
Permutations
•
This
can
also
be
useful
for
permutation
calculations:
To
select
and
rank
a
subset
of
3
items
out
of
5:
5
P
3
=
5!
/
(5
‐
3!)
=
60
Your
TI
has
a
built
in
function
for
this:
[2
nd
][
‐
]
=
[
n
P
r
]
5
P
3
=
5
[2
nd
][
n
P
r
]
3
[=]
60
CFA Society Los Angeles
36
