sample mean

A physical education teacher reported that the mean height of all the girls of grade 10 was 164.5 cm. From a random sample of 20 girls selected from a school, it was observed that the mean height was 167.5 cm and the standard deviation was 6 cm. Test the teacher's repo..

The report of a municipal corporation states that the average monthly electricity bill of a household in the city is $75. To test this report, a researcher selected a sample of 120 residential electricity bills and found the mean as $76.50 with a standard deviation of $15. At &a..

A researcher wishes to estimate the average daily wage (industrial composite) of industrial workers. A previous study showed that the standard deviation is $23. How large a sample must be selected if he wants to be 99% confident of getting an interval that contains the true mean..

A cigarette manufacturer claims that the nicotine content of its cigarette is 1.05 mg. A sample of 20 cigarettes were selected and found that the mean nicotine content is 1.40 mg with a standard deviation of 0.77 mg. At α = 0.05, is there enough evidence to reject the manu..

A civil engineer in U.S. earns an average annual salary of $40,280 as reported in an economic survey. The mean salary of a sample of 20 civil engineers was found to be $40,000 with a standard deviation of $353. At α = 0.05, what is the test value? Is the survey report true..

What is the formula to find the z score for the difference between two population means, if X 1 and X 2 are the sample means, s 1 2 and s 2 2 are the sample variances and n 1 and n 2 are the size of the samples? (Assume both n 1 and n 2 are greater ..

A technician requires to perform preventive maintenance on electronic goods. The mean time is 72 minutes and the standard deviation is 1 hour. For a sample of 45 goods, what is the probability that their average maintenance time exceeds 50 minutes? => 0.071 or 9.929 or 0.9929 or..

A gas lighter manufacturer claims that the lifespan of his gas lighter has a mean of 48 months and a standard deviation of 6 months. A sample of 50 gas lighters are tested by a consumer advocacy group. Assuming the manufacturer's claims are true, what is the probability that it ..

From a random sample of 36 restaurents in a particular city, the average cost per dinner was reported as $26.50. What is the test value if the population mean is $25 with standard deviation of $4.40 and α = 0.01? Can we say that the sample comes from this populat..

The prices of 1 gallon of premium gasoline in U.S dollars in a sample of seven foreign countries is shown. What is the point estimate for the mean? Find the 98% confidence interval of the mean for the prices of 1 gallon of premium gasoline in U.S. 3.80, 3.20, 3.80, 3.5..