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68
<""unction
Ke\'~
press
D
rn,
the mean of the values
of
x is
calc ulated
using the
data
in
storage
registers
R3
(n)
and
R 7 (lx)
and
the
form ula:
n
-
I "
x
= -
L.J
Xi
n
i
=
1
The
easiest
way to
acc umulate
the required
data
in
the
appli-
cable
registers is
through the
use of
the
Ell
key
as
de
scribed
a bove.
However, the required
data
may
also
be stored
directly
in
storage
registers
R3
(n)
and
R7 (lx)
,
if desired.
Example:
A
survey
found
ten of the
wealthiest
persons in
the
U nited States
to
have
the following
ages:
62
84
47
58
68
60
62
59
71
73
To
find
the
ave rage
(mean)
age of
this
sample
of
wealthy
persons:
Press
Display
0.00
1
Storage registers
~-'='----'
62
Ell
,
84
Ell
,
47
Ell
,
58
Ell
,
68
Ell
,
60
Ell
,
62
Ell
,
59
Ell
'
and
X-register
cleared to
zero.
71
Ell
,
73
Ell
1,-
1
-
0 .-00
- ---,1
N umber
of
entries
.
D
rn
1
64.40
1
A verage
(mean)
age
in
yea
rs.
Standard Deviation
The standard deviation (a
meas ure of
dispersion
around
the
mean)
is calc ulated usi
ng
data in the
applicable storage
registers
and
the
@]
(standard
deviation)
key. Pressing
@]uses the
data
in
registers
R3lll),
Ru
(lx
2
),
and
R7 (lx) to
calculate
the
standard
deviation
according
to
the
formula:
n-I
S
=
J"
2
(lX)2
x
L.J
x
-
- -
n
For example
,
to
obtain
the
sample
deviation
in
the
above
problem
:
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