Automobile Tires

1. (TCO 3) The grades of 22 students are listed below. Use the stem & leaf to determine the shape of the distribution. Choose the best answer. 4 | 7 5 5 | 1 7 5 6 | 5 6 7 8 9 7 | 1 6 7 8 8 9 8 | 2 4 7 6 9 | 4 7 a. The data is symmetric b. The data is skewed to the right c. The data is skewed to the left d. The data is bimodal 

2. A researcher is interested in studying people’s mean age in a certain region. If the population standard deviation is known to be 8 years and 1.5 year of error margin is allowed, find the minimum simple size the researcher needs to use, knowing that he is going to conduct his study using 95% confidence level.  110

3. Horse race time is found to be normally distributed with a mean value of 10 minutes and a standard deviation of 2 minutes. Horses whose race time is in the top 5% will not be eligible to participate in a second round. What is the lowers race time that makes a horse losses his eligibility to participate in a second round?  13.29 minutes

4. A class containing 15 students 5 of them are females. In how many ways can we select a group of 4 male students?  210 ways

5. Research shows that the life time of Everlast automobile tires is normally distributed with a mean value of 70,000 miles and a standard deviation of 7,000 miles. What is the probability of having a tire that lasts more than 80,000 miles? 0.0766 

6. A research shows that employee salaries at company XYX, in thousands of dollars, are given by the equation y-hat= 48.5 + 2.2 a + 1.5 b where ‘a’ is the years of experience, and ‘b’ is the education level in years. In thousands of dollars, predict the salary for an employee with 5 years experience and 16 years education level.  83.5

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