Formula Card for Chapters Five and Six
For Problems Dealing With the Normal Distribution (they say normally distributed
in the directions…)
There are three cases
1.
Directions say: Find the probability of randomly selecting a …

Draw the bell curve, label the mean, and standard deviation

Put a Z number line and an X number line at the bottom of the curve

Shade the desired area that you are looking for

Convert your x – score into a zscore using
X
Z
μ
σ

=

Look your zscore up on the table from the book (that is the area from your z
score to the mean on the curve)

If necessary perform the arithmetic needed to get your desired area
2.
Directions say: Find the probability of randomly selecting n …that have an average …

Draw the bell curve, label the mean, and standard deviation **do not forget that
for this problem the stan. dev. becomes
X
n
σ
σ
=

Put a Z number line and an
X
number line at the bottom of the curve

Shade the desired area that you are looking for

Convert your
X
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 Winter '08
 STAFF
 Normal Distribution, Probability, Standard Deviation, Bell Curve, Stan. Dev.

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