It has been suggested that abnormal male children

1. It has been suggested that abnormal male children tend to occur more often in children born to older than average mothers. Case histories of 20 abnormal males were obtained. The mean age of the 20 mothers of these children was 31.45 and the sample standard deviation was 9.049 years. It is known that the mean age at which mothers in the general population give birth is 28 years. Does the sample give sufficient evidence to support the claim that the mean age of mothers of abnormal male children is greater than 28 years? Use 0.05 . Assume the ages of mothers of abnormal male children have a normal distribution.

2. A light bulb manufacturer guarantees that the mean life of a certain type of light bulb is 750 hours. A random sample of 36 light bulbs has a mean life of 735 hours. If we assume that the population standard deviation is 45 hours, is there sufficient evidence to suggest that the mean life of these light bulbs is actually less than the manufacturer claims? Let 0.05.

3. A survey showed that among 785 randomly selected subjects who completed four years of college,

144 of them are smokers. Use a 0.01 significance level to test the claim that the rate of smoking among those with four years of college is less than the 27% rate for the general population.

4. Historically, the mean assembly time for the Enyaw Kralc automobile has been 38 hours. A modification to the assembly procedure is made. A random sample of 47 Kralc automobiles yields an average assembly time of 37.5 hours and a standard deviation of 1.2 hours with the new procedure .

Test the claim that the average assembly time has been reduced with the new procedure. Use


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