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UTPN(<mean>,<variance>,<value>)
This function, the ‘Upper-Tail Probability (Normal)’, gives the probability that a normal random variable is
greater than or equal to the value supplied. Note that the variance must be supplied, NOT the standard
deviation.
Eg. 1.
Find the probability that a randomly chosen individual is
more than 2 meters tall if the population has a mean
height of 1.87m and a standard deviation of 10.4cm
2m
x
=
1.87
m
,
σ
=
0.104
m
2
⇒
σ
=
0.010816
Ans: P(height>2m) = 0.1056
Eg. 2.
The population of Year 12 Applicable Mathematics students had a mean exam score of 65%
and a standard deviation of 14%. What two scores will cut off the top and bottom 10% of
students?
0·1
0·1
65%
i.e. Find
x
0
such that
P x x
0
)
=
0
1
(
>
⋅
Using the Solve aplet (right) we can reverse the normal direction of the
UTPN
function.
Enter the expression to be solved for into the
SYMB
view as shown
above, then switch to the numeric view. Enter a guess of 0.8 (80%) and
then press
.
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