Statistics - Confidence Intervals for an electrical firm

9.4 An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm.

9.6 The heights of a random sample of 50 college students showed a mean of 174.5 centimeters and a standard deviation of 6.9 centimeters.
(a) Construct a 98% confidence interval for the mean height of all college students.

(b) What can we assert with 98% confidence about the possible size of our error if we estimate the mean height of all college students to be 174.5 centimeters?

9.10 An efficiency expert wishes to determine the average time that it takes to drill three holes in a certain metal clamp. How large a sample will he need to be 95% confident that his sample mean will be within 15 seconds of the true mean? Assume that it is known from previous studies that s=40 seconds.

9.14 A random sample of 10 chocolate energy bars of a certain brand has, on average, 230 calories with a standard deviation of 15 calories. Construct a 99% confidence interval for the true mean calorie content of this brand of energy bar. Assume that the distribution of the calories is approximately normal.

9.16 A random sample of 12 graduates of a certain secretarial school typed an average 79.3 words per minute with a standard deviation of 7.8 words per minute. Assuming a normal distribution for the number of words typed per minute, find a 95% confidence interval for the average number of words typed by all graduates of this school.

Are Confidenceintervals part of descriptive statistics or inferential statistics- why? Why would we use confidenceintervals instead of point estimates? Give an example of the use of a confidence interval and why you would prefer it over point estimates in your example.

In a statistics lecture, students are asked whether or not they enjoyed doing statistics. Random sample of 50 students was taken and 30 of them said that they enjoyed doing statistics. The lecturer claimed that more than 50% of the students enjoyed doing statistics.
(i) Test, at the 5% level of significance, whether or not

What do we mean by confidenceintervals - provide an example that illustrates your answer.
Suppose we were to apply 95% and 99% confidence to your study results.. how might your result differ and why?

Confidenceintervals are used to help you get a better feel for your estimated value. Confidenceintervals are like nets. You don't know what the TRUE proportion value is so you throw a net (find a confidence interval based upon a survey). The confidence level indicates the percentage of times your net would "catch" the true pop

A criminology professor has been teaching graduate and undergraduate statisticsfor a few years. Her records show that the overall mean for final exam scores is 82 with a standard deviation of 10. The professor believes that this year's class is superior to her previous classes. She decides to conduct a test on the 25 students

See the data in the attached file and answer the following questions.
Question 1
Construct a 95% confidence interval for an average value of y given that x = 4. Remember the format is (x.xx, x.xx)
Question 2
Construct a 95% prediction interval for y given that x = 4.

We will be constructing confidenceintervalsfor the proportion of each color as well as the mean number of candies per bag.
Construct a 95% Confidence Interval for the proportion of blue M&Ms® candies.
Construct a 95% Confidence Interval for the proportion of orange M&Ms® candies.
Construct a 95% Confidence Interva

1. What do confidenceintervals represent? What is the most controllable method of increasing the precision (narrowing) of the confidence interval? What percentage of times will the mean (population proportion) not be found within the confidence interval?
2. As a sample size approaches infinity, how does the t distribution co