SOLUTION: I am having trouble with this: I want to understand how to find the standard deviation given average age of cars 19.4 years, there is normal distribution, 20% cars
are older than
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are older than
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Question 431251: I am having trouble with this: I want to understand how to find the standard deviation given average age of cars 19.4 years, there is normal distribution, 20% cars
are older than 22.8 years find standard deviation Answer by Edwin McCravy(20056) (Show Source):
P(z > ) = .20
P(z > ) = .20
Next we find the z-score which has .20 of the area to
the right of it.
It will therefore have .5-.20 or .30 of the area between the
center line and the z-score.
So you will look through the body of your table until
you find the closest entry to .30.
The closest entry to .30 is .2995, which corresponds to
the z-score of 0.84
[Some books have a normal table that gives values from
the extreme left side. In that case you will look for
the closest value to .80 and that will be 0.7995, and
that will also correspond to the z-score of 0.84].
So Solve this equation for :
Solve that and get
Edwin
