It has been suggested that abnormal male children tend to be born to older-than-average parents. Case histories of 20 abnormal males were obtained, and the ages of the 20 mothers were as follows:

The mean age at which mothers in the general population give birth is 28.0 years.
a. Calculate the sample mean and standard deviation.
b. Does the sample give sufficient evidence to support the claim that abnormal male children have older than- average mothers? Use a = 0.05 Assume ages have a normal distribution.

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