A random sample of size 25 from a normal population has mean 47.5 and standard deviation 8.4. Does this information tend to support or refuse the claim that the mean of the population is 42.1?

A survey among freshmen at a certain university revealed that the number of hours spent studying the week before final exams was normally distributed with mean 25 and standard deviation 9.  Between what two values are the middle 80% of the hours spent studying?

Per the Barron's report the average weeks unemployed is 21.5 (population mean) with a population standard deviation of 5 weeks and a sample of 55. Calculate the standard error of the mean to two decimals.

Suppose that a sample of size 52 is drawn from a population with mean 23 and standard deviation 39 . Find the value of , the standard deviation of the distribution of sample means.

The ages of a group of 138 randomly selected adult females have a standard deviation of 17.5 years. Assume that the ages of female statistics students have less variation than ages of females in the general population, so leto= 17.5 years for the sample size calculation. How many female statistics student ages must be obtained in order to estimate the mean age of all female statistics students? Assume that we want 95% confidence that the sample mean is within one-half year of the population mean. Does it seem reasonable to assume that the ages of female statistics students have less variation than ages of females in the general population? The required sample size is (Round up to the nearest whole number as needed.)

According to Current Population Reports, the population distribution of number of years of education for self-employed individuals in the United States has a mean of 13.6 and a standard deviation of 3.0.  Find the mean and standard error of the sampling distribution of ȳ for a random sample of  9 residents.

If IQ scores are normally distributed with a mean of 100 and a standard deviation of 15, what is P85?