Discussion Section 227
10/05/10
Chapter 7: Probability
The normal curve has known m
under the curve and use it to co
The Z score distribution forms a
from the population between +
Using the Unit Normal Table
1.
The table gives us propo
2.
The table has 4 columns
A.
Z score
B.
proportion in body
C.
proportion in tail
D.
proportion between
3.
To find the probability o
to a Z score and then lo
4.
Because the distribution
table.
ty, Z scores, and the Sampling Distribution of the M
mathematical properties and so it is possible to comp
ompute probabilities.
a normal curve. What is the probability of obtaining
+1 and 1 SD?
.68
ortions of areas under the normal curve for every Z
s (from left to right):
n mean and Z
of obtaining any individual score, we first convert th
ook up the appropriate proportion in the Unit Norma
n is symmetrical, we can ignore negative signs when
Mean
pute the area
an individual
score.
he raw score
al Table.
n using the
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Example 1
:
Population with µ = 84, σ = 6
What is the probability of obtain
1.
Draw sketch:
a.
Draw normal curve.
b.
Add in the mean an
c.
Add the score of int
d.
Shade the appropria
2.
Convert raw score to Z s
Z = (9684)/6 = 2
3.
Look up proportion in th
we don’t care about ne
(proportion in the tail).
Now we write the state
P(Z>2) = .0228 or 2.28%
Example 2:
In the same distribution (µ=84,
1.
Draw a sketch:
ning a score of more than 96? P(X>96)
.
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 Fall '10
 Fairchild
 Normal Distribution, Standard Deviation

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