Calculating
a value
for the value of P( x <
)
1. Finding x:
The
TI-83/84 is equiped with a built in function called invNorm (p, ,
).
It computes where p = P(x <
)
which is the area under the standard normal curve between to the left of
.
This is also the x-value for the pth percentile.
To
calculate x for a p = 0.9, =500
and
=
100, that is the area under the normal curve is 0.9 and this area is to the left
of some x value, press 2nd VARS [DISTR], ARROW DOWN to select 3:invNormal(,
and then press ENTER.
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After area: type
. 9 ENTER, after : type 500 ENTER and after
: type 100 ENTER, and then press ENTER again. See the results below.
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Thus 90% of the x values lie below x = 628.2.