A company in Maryland has developed a device that can be attached to car engines,which it believes will increase the miles per gallon that cars will get.The owners are interested in estimating the difference between mean mpg for cars using the device versus those that are not using the device.The following data represent the mpg for independent random samples of cars from each population.The variances are assumed equal and the populations normally distributed. Given this data,what is the critical value if the owners wish to have a 90 percent confidence interval estimate?
A)t = 2.015
B)t = 1.7823
C)z = 1.645
D)z = 1.96

Question

A company in Maryland has developed a device that can be attached to car engines,which it believes will increase the miles per gallon that cars will get.The owners are interested in estimating the difference between mean mpg for cars using the device versus those that are not using the device.The following data represent the mpg for independent random samples of cars from each population.The variances are assumed equal and the populations normally distributed.  Given this data,what is the critical value if the owners wish to have a 90 percent confidence interval estimate?
A)t = 2.015 
B)t = 1.7823 
C)z = 1.645 
D)z = 1.96

Quizplus · Accepted Answer

Since the sample size is less than 30 and the population standard deviation is unknown, we use a t-distribution. The critical value for a 90% confidence interval with 18 degrees of freedom (n1 + n2 - 2) is 1.7823, which is closest to option B.

A Company in Maryland Has Developed a Device That Can