Answer to Question #149507 in Statistics and Probability for NOR ZAHIRAH

Question

HYPOTHESIS TESTING AND CONFIDENCE INTERVAL

3) Records on a fleet of trucks reveal that the average life of a set of spark plugs is normally distributed with a mean of 22,100 miles. The fleet owner purchased 18 sets and found that the sample average life was 23,400 miles; the sample standard deviation was 1,412 miles. To decide if the sample data support the company records that the spark plugs average 22,100 miles, state your decision in terms of the null hypothesis. Use a 0.05 level of significance.

4)A local grocery store wants to estimate the mean daily number of gallons of milk sold to customers. Assume the number of gallons sold follows the normal distribution, with a population standard deviation of 5.10 gallons. A random sample of 60 days shows that the mean daily number of gallons sold is 10.00. What is the point estimate of the population mean?

Answer 1

3.A)

Null hypothesis Ho : u = 22100

Alternate hypothesis Ha : u not equal to 22100

B)

As the population s.d is unknown here and we are given with sample s.d as the best estimate.

We will use t table to estimate the critical values.

Degrees of freedom is = n-1 = 17

For 17 dof and 0.05 alpha.

Critical values

4.The point estimate of the population mean is 10 gallons.

[(10-2.575*5.10/sqrt((60)), 10+ 2.575*5.10/sqrt((60))])

= [8.3, 11.7]