Continuous Random Variables and Sampling Distributions
Needs to be labeled example3.1 Question 1a.b.c.3.1 Answer the following questions in a Word document: What makes the normal distribution a probability distribution?In a normal distribution, what percentage of the area under a normal curve is between µ - σ and µ + σ?In a normal distribution, what percentage of the area under a normal curve is between µ - σ and µ + 2σ?Suppose you are interested in how long it takes to get your food at a restaurant. Now, suppose this distribution is approximately normal with an average of eight minutes and a standard deviation of two minutes. If you made a control chart for this data, what would be the highest control limit?Using the above scenario, suppose someone gets the food after exactly 11 minutes. How many standard deviations from the mean is this value of 11?Using the above scenario, what is the probability that someone would get the food after more than 11 minutes?Using the standard normal distribution, find the area below z=-0.8.Using the standard normal distribution, find the area above z=-0.8.Using the standard normal distribution, find the area between z=-0.8 and z=2.1. 3.2 The heights of 18-year-old men are approximately normally distributed with a mean (µ) of 68 inches and a standard deviation (σ) of 3 inches. What is the probability that an 18-year-old man selected at random is taller than 70 inches? Suppose that, instead of randomly selecting one 18-year-old male, you randomly select 10 18-year-old males. What is the probability that the average height for these 18-year-old males is more than 70 inches?The average age for employees at an amusement park is 24 years old with a standard deviation of 2.5 years. Suppose random samples of 40 employees are selected. What would the distribution of average ages from samples of this size look like? Why?Use the above amusement park scenario to answer the following questions: What would the average be for all sample means from samples of this size?What would the standard error be for all sample means from samples of this size?What is the probability if you randomly selected 40 employees and averaged their ages together that the sample mean would be between 23 and 25 years? 3.3 What percentage of the area under the normal curve lies A normal distribution has mean = 12 and standard deviation = 3. To the left of the mean?Between μ – 2σ and μ + 2σ?More than three standard deviations above the mean? 2. Over an entire summer, an amusement park gets an average of 21.7 people per day that have to go to the infirmary. Some days it is higher than this. Some days it is lower than this. The standard deviation is 4.2. The distribution for the amount of people treated is approximately normal. For a 10-day period, here are the number of people treated each of those 10 days:For a 10-day period, here are the number of people treated each of those 10 days: Day 1 2 3 4 5 6 7 8 9 10 Number treated 25 19 17 15 20 24 30 19 16 23 Make a control chart for the daily number treated, and plot this data on that chart. Do the data indicate that the number of people treated is “in control”? Explain your answer. Day 1 2 3 4 5 6 7 8 9 10 Number treated 20 15 12 21 24 28 32 36 35 37 Make a control chart for the daily number treated, and plot this data on that chart. Do the data indicate that the number of people treated is “in control”? Explain your answer. The z-score corresponding to x = 18.Find the raw score corresponding to z = -1.5. 4. John received an 85% on a history test and a 78% on a Spanish test. For the history test, the class mean was 82% and standard deviation 10. For the Spanish test, the class mean was 74% and standard deviation 2. On which test did he do better relative to the rest of the class? 5. Find the specified areas under the standard normal curve: To the left of z = .56To the right of z = 1.3To the right of z = -2.2Between z = -1.2 and z = 2.1P(-1.78 < z < -1.23) 6. If the mean of a normal distribution is 40 and the standard deviation is 4, find P(38 < x < 46). 7. Find z such that... 10% of the standard normal curve lies to the right of z.90% of the standard normal curve lies between -z and z. 8. A local band is going on a U.S. Summer tour, and they average about 2,000 people per concert, with a standard deviation of about 400. Assume that these concert numbers follow a normal distribution. If a concert is selected at random, what is the probability that there were more than 2,500 people at that concert?If a concert is selected at random, what is the probability that there were less than 1,800 people at that concert?If a concert is selected at random, what is the probability that there were between 1,800 and 2,500 people at that concert?For a concert to be in the top 10% as far as attendance, at least how many people would need to attend the concert? 9. Define what a sample statistic is. Give three examples of sample statistics from your everyday life. 10. Define what a sampling distribution is. Using one of your three examples from the previous problem, explain a possible sampling distribution. 11. Define what the standard error of a sample distribution is. 12. The heights of 18-year-old females are approximately normally distributed with a mean of 64 inches and a standard deviation of 3 inches. What is the probability that an 18-year-old woman selected at random is between 63 and 65 inches tall? Suppose samples of 25 18-year-old females are taken at a time. Describe the sampling distribution of the sample mean and compute the mean and standard deviation of this sampling distribution. Find the z-score corresponding to a sample mean of 66 inches for a sample of 25 females. Find the probability that a sample mean from a sample like this would be higher than 66 inches. Based on the probability found in the previous part, would a sample like this be unusual? If a random sample of 25 18-year-old females is selected, what is the probability that the mean height for this sample is between 63 and 65 inches?