Finding Cumulative Probabilities
Submitted by gfj100 on Wed, 11/11/2009  10:43
Using the Standard Normal Table in the appendix of textbook or see a copy at
Standard
Normal Table
Table A.1 in the textbook gives normal curve cumulative probabilities for standardized scores.
•
A
standardized score
(also called
z
score) is
.
•
Row labels of Table A.1 give possible
z
scores up to one decimal place. The column
labels give the second decimal place of the
z
score.
The cumulative probability for a value equals the cumulative probability for that value's
z
score.
Here, probability speed less than or equal 73 mph = probability zscore less than or equal 1.60.
How did we arrive at this zscore?
Example
In our vehicle speed example, the standardized scores for 73 mph is
.
We look in the ".00" column of the "1.6" row (1.6
plus
.00 equals 1.60) to find that the
cumulative probability for z = 1.60 is 0.9452, the same value we got earlier as the cumulative
probability for speed = 73 mph.
Example
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 Spring '11
 AndyRegards
 Normal Distribution, Standard Deviation

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