Suppose taxi fare from Logan Airport to downtown Boston is known to be normally distributed with a standard deviation of $2.50. The last seven times John has taken a taxi from Logan to downtown Boston, the fares have been $22.10, $23.25, $21.35, $24.50, $21.90, $20.75, and $22.65. What is a 95% confidence interval for the population mean taxi fare?

An IQ test has a mean of 96 and a standard deviation of 15. Which is more​ unusual, an IQ of 81 or an IQ of 120​?

Entrance exam scores at Cititon University are normally distributed with a mean of 552 and a standard deviation of 29. If scholarships are awarded to the top 10% of scores, what is the minimum score needed to guarantee a scholarship?

A report about how American college students manage their finances includes data from a survey of college students. Each person in a representative sample of 793 college students was asked if they had one or more credit cards and if so, whether they paid their balance in full each month. There were 500 who paid in full each month. For this sample of 500 students, the sample mean credit card balance was reported to be $825. The sample standard deviation of the credit card balances for these 500 students was not reported, but for purposes of this exercise, suppose that it was $205. Is there convincing evidence that college students who pay their credit card balance in full each month have a mean balance that is lower than $907, the value reported for all college students with credit cards? Carry out a hypothesis test using a significance level of 0.01.   State the appropriate null and alternative hypotheses. H0: ? = 907 Ha: ? < 907 H0: ? = 907 Ha: ? > 907      H0: ? < 907…

A study shows that Michigan teachers have measures of job dissatisfaction that are normally distributed with a mean of 3.80 and standard deviation of 0.95. If subjects with scores above 4.0 are to be given more tests, what percentage will fall into that category?

Butt-to-knee length is approximately normally distributed with a mean of 23.1 inches and a standard deviation of 1.2.  Theater seats are designed to be comfortable for as many adults as possible.  If the seats are required to fit the middle 80% of the population, the seat must be comfortable for what butt-to-knee length range?

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