3. A large group of students took a test in English and the final grades have a mean of 75 and a standard deviation of 8. If we can approximate the distribution of these grades by a normal distribution. What percentage of the students
(i) Scored higher than 70?
(ii) Should pass the test(grades 2 >= 60)
(iii) Should fail the test(grades <60?
4. An industrial designer wants to determine the average amount of time it takes an adult to assemble an"easy to assemble" toy. A sample of 56 times yielded an average time of 20,5 minutes, with a sample standard deviation of 6.25 minutes.
(iii)Find the 95% confidence interval for the mean assembly time.
(iv)Find the 99% confidence interval for the mean assembly time.
5. 450 workers were selected at random from a district. Their mean income was $. I 40 per month. With standard deviation of $. 14.5. Do you believe that the average income of the workers community in the district is $ 135?
(i) Scored higher than 70?
(ii) Should pass the test(grades 2 >= 60)
(iii) Should fail the test(grades <60?
4. An industrial designer wants to determine the average amount of time it takes an adult to assemble an"easy to assemble" toy. A sample of 56 times yielded an average time of 20,5 minutes, with a sample standard deviation of 6.25 minutes.
(iii)Find the 95% confidence interval for the mean assembly time.
(iv)Find the 99% confidence interval for the mean assembly time.
5. 450 workers were selected at random from a district. Their mean income was $. I 40 per month. With standard deviation of $. 14.5. Do you believe that the average income of the workers community in the district is $ 135?
