Posted by Anonymous on Saturday, November 3, 2012 at 9:40pm.
The average age for licensed drivers in the county
is μ 40.3 years with a standard deviation of
13.2 years.
a. A researcher obtained a random sample of n 16
parking tickets and computed an average age of
M 38.9 years for the drivers. Compute the zscore
for the sample mean and find the probability of
obtaining an average age this young or younger
for a random sample of licensed drivers. Is it
reasonable to conclude that this set of n 16
people is a representative sample of licensed
drivers?
b. The same researcher obtained a random sample of
n 36 speeding tickets and computed an average
age of M 36.2 years for the drivers. Compute the
zscore for the sample mean and find the probability
of obtaining an average age this young or
younger for a random sample of licensed drivers.
Is it reasonable to conclude that this set of n 36
people is a representative sample of licensed
drivers?

statistics  PsyDAG, Sunday, November 4, 2012 at 1:27pm
Z = (mean1  mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√n
If only one SD is provided, you can use just that to determine SEdiff.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability of the Z scores.
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