In: Statistics and Probability
A tow truck company suspects that the lifespan of certain tires is less than the 28,000 miles they were offered. To verify if its suspicion is true, the company purchases 40 tires, places them in its trucks and measures the life of each one. The results are presented in the rate below. Presumed known standard deviation = 1300 miles
26579 | 27965 | 26868 | 25070 | 26488 |
25834 | 27355 | 28039 | 32237 | 25523 |
28331 | 29103 | 24439 | 32850 | 28942 |
27474 | 27618 | 25645 | 27497 | 28183 |
27475 | 27697 | 28524 | 27704 | 26873 |
27232 | 31633 | 29363 | 26857 | 28017 |
27396 | 26982 | 28007 | 26293 | 25828 |
28256 | 25679 | 22594 | 31000 | 24208 |
If we perform a hypothesis test with α = 0.1,
to. What can we conclude? Is the company correct in its suspicions? Respond based on evidence - Clearly define hypotheses, areas of acceptance and rejection, test statistic and CONCLUDE in complete sentence
b. If we wanted to construct a confidence interval for µ with an error of not more than 25 miles, what sample size should we use?
c. If the actual average is 27,800 miles, what would be the probability of making a type II error? What would it mean in this case to make a type II error?
26579 |
25834 |
28331 |
27474 |
27475 |
27232 |
27396 |
28256 |
27965 |
27355 |
29103 |
27618 |
27697 |
31633 |
26982 |
25679 |
26868 |
28039 |
24439 |
25645 |
28524 |
29363 |
28007 |
22594 |
25070 |
32237 |
32850 |
27497 |
27704 |
26857 |
26293 |
31000 |
26488 |
25523 |
28942 |
28183 |
26873 |
28017 |
25828 |
24208 |
a.
Mean = 27491.45 miles, standard deviation = 1300 miles
Ho: The lifespan of certain tires is equal to the 28,000 miles
H1: The lifespan of certain tires is less than the 28,000 miles
Then, = = -2.474
Then, t(39,0.1) = -1.304 (one-tailed)
Here, -2.474 < -1.304
So, we reject Ho or can say that the lifespan of certain tires is less than the 28,000 miles.
b. Now, error = 25 miles = t*s/sqrt(n) ; sqrt(n) = 1.304 * 1300 / 25 ; n= 4597.92 or 4598 trucks will be inspected
c. At apha = 0.1, and actual mean 27800, cohen's d = 0.24
then, beta = 1 - 0.82 = 0.18 (i am not sure for this one, do let me know)