Posted by Barbara on Tuesday, June 8, 2010 at 1:45pm.
A local tire store suspects that the mean life of a new discount tire is less that 39,000 miles. To check the claim, the store selects randomly 18 of these new discount tires. When they are tested, it is found that the mean life is 38,250 miles with a sample standard deviation s=1200 miles. Assume the distribution is normally distributed.
Use the critical value to method from the normal distribution to test for the population mean u. Test the company's claim at the level of significance a=0.05

statistics  MathGuru, Tuesday, June 8, 2010 at 10:44pm
Use a onesample ztest.
z = (sample mean  population mean)/(standard deviation divided by the square root of the sample size)
With your data:
z = (38250  39000)/(1200/√18) = ?
Finish the calculation.
Check a ztable at .05 level of significance for a onetailed test.
If the ztest statistic exceeds the critical value from the ztable, reject the null. If the ztest statistic does not exceed the critical value from the ztable, do not reject the null.
I hope this will help get you started.
Answer This Question
Related Questions
 math  a tire manufacturer believes that the tread life of its tires are ...
 statistics  According to internal testing done by the GetAGrip tire company, ...
 Statistics  Wrong tire pressure can increase tire wear and decrease gas mileage...
 Statistics  A purchasing agent for a trucking company is shopping for ...
 Statistics  A purchasing agent for a trucking company is shopping for ...
 statistics  one of the major U.S. tire makers wishes to review its warranty for...
 statistic  one of the major U.S. tire makers wishes to review its warranty for ...
 Statistics  According to internal testing done by the GetAGrip tire company, ...
 statistics  Assume that Acme Tires sells their high performance tires for $180 ...
 statistics  at the tire store, 10 out of every 100 tires are defective. if your...
More Related Questions