Question

The Rogers Bicycle & Gun Company sells a light, new road tire that they advertise to go over 5,000 miles before it must be replaced. Several of the company’s customers have complained that the new tire does not actually make it to 5,000 miles. The company decided to test the tires. They tested a sample of 25 tires and found the average tire life to be 4,300 miles with a standard deviation of 500 miles. It will cost the company money if they have to change their advertisements, but they want to keep their customers’ trust. They have decided to restate their advertised claim only if there is significant evidence (α = 0.05) to infer that the tire life is less than 4,500 miles. What is the critical value for this problemQ

Answer 1

The critical value for this test is tc=-1.71.

Explanation:

We have to calculate the critical value for this hypothesis test.

We have a sample of size n=25, with mean M=4300 and standard deviation s=500.

The population standard deviation is not known, so we will use the sample standard deviation as an estimation and use a t-test.

To calculate the critical value for this problem, we need to know the type of test, significance level and, because is t-test, the degrees of freedom:

The test is one-sided (left tail) test.

The significance level is 0.05.

The degrees of freedom are df=n-1=25-1=24.

Then, using a table for the t-students distribution, we get the critical value:

`P(t<t_c)=0.05\Rightarrow t_c=-1.71`

The critical value for this test is tc=-1.71.