Casio fx-9860GII - Page 54

Using a graphic display calculator
© Oxford University Press 2012: this may be reproduced for class use solely for the purchaser’s institute
Casio fx-9860GII
Example 58
A random variable X is normally distributed with a mean of 75 and a standard
deviation of 12 or X ~ N(75, 12
2
). If P (X < x) = 0.4, fi nd the value of x.
Press
MENU
and choose 2: STAT and press
EXE
.
Press
F5
DIST
F1
NORM
F3
InvN to use the Inverse Normal function.
Press
F2
Var.
Enter Tail as Left (
F1
), Area as 0.4, σ as 12 and μ as 75.
Press
EXE
.
So if P (X < x) = 0.4 then x = 72.0 (to 3 sf).
Example 59
A random variable X is normally distributed with a mean of 75 and a
standard deviation of 12 or X ~ N(75, 12
2
).
If P ( X > x) = 0.2, fi nd the value of x.
Press
MENU
and choose 2: STAT and press
EXE
.
You are given a lower-
tail probability so you
should choose ‘Left’.
You should enter
the values: Area
(probability),
σ and μ ,
in order.
You are given an
upper-tail probability
so you should choose
‘Right’.
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