Question

10. Stock Prices A random sample of stock prices per share (in dollars) is shown. Find the 90% confidence interval for the variance and standard deviation for the prices. Assume the variable is normally distributed. Chapter 7 Confidence Intervals and Sample Size 404 3. Using Table G. find the values for en and icht a a0.05, n 12 b a 0.10,n-20 a0.05, n27 12.00 28.37 47.50 13.88 7.50 53.81 28.25 10.87 26.69 43.00 75.37 3.81 45.12 13.62 d a0.01,n=6 60.50 28.00 e a0.10, n= 41 6,94 14.75 46.12 4, Lifetimes of Wristwatches Find the 90% confidence interval for the variance and standard deviation for the lifetimes of inexpensive wristwatches if a random sample of 24 watches has a standard deviation of 4.8 months. Assume the variable is normally distributed. Do you feel that the lifetimes are relatively consistent? 40.25 Source: Pisburgh Tribune Review 11. Cost of an Operation A medical researcher surveyed 11 hospitals and found that the standard deviation f the cost for removing a person's gall bladder was $s Assume the variable is normally distributed. Based this, find the 99% confidence interval of the population variance and standard deviation. 5. Carbohydrates in Yogurt The number of carbo- hydrates (in grams) per 8-ounce serving of yogurt for each of a random selection of brands is listed below. Estimate the true population variance and standard deviation for the number of carbohydrates per 8-ounce serving of yogurt with 95% confidence. Assume the variable is normally distributed. 12. Home Ownership Rates The percentage rates of home ownership for 8 randomly selected states are listed helouw Estimate the population variance and standard deviation for the percentage rate of home ownership with 99% con- fidence. Assume the variable is normally distributed. 17 42 41 20 39 41 35 15 43 25 38 33 42 23 17 25 34 70.9 73.9 66.0 75.8 63.4 68.5 73.3 65.9 Source: World Almanac 6. Carbon Monoxide Deaths A study of generation related carbon monoxide deaths showed that a random sample of 6 recent years had a standard deviation of 4.1 deaths per year. Find the 99% confi- 13. Calories in a Standard Size Candy Bar Estimate the standard deviation in calories for these randomly selected standard-size candy bars with 95% confi- dence. (The number of calories is listed for each.) Assume the variable is normally distributed. dence interval of the variance and standard deviation. Assume the variable is normally distributed. Source: Based on information from Consumer Protection Safety Commission 220 220 240 210 230 280 275 260 240 7. Pacemaker Batteries A manufacturer of pacemakers wants the standard deviation of the lifetimes of the bat- teries to be less than 1.8 months. A sample of 20 batteries had a standard deviation of 1.6 months. Assume the vari- able is normally distributed. Find the 95% confidence interval of the standard deviation of the batteries. Based on this answer, do you feel that 1.8 months is a reason- able estimate? 220 240 230 260 280 14. SAT Scores Estimate the variance in mean mathemat ics SAT scores by state, using the randomly selected scores listed below, Estimate with 99% confidence. Assume the variable is normally distributed. 490 502 543 211 572 Source: World Almanac 2012. 209 499 565 500 469 8. Age of College Students Find the 90% confidence interval for the variance and standard deviation of the ages of seniors at Oak Park College if a random sample of 24 students has a standard deviation of 2.3 years. Assume the variable is normally distributed. 550 515 15. Daily Cholesterol Intake The American Heart As sociation recommends a daily cholesterol intake of less than 300 mg. Here are the cholesterol amounts i a random sample of single servings of grilled meats Estimate the standard deviation in cholesterol with 95% confidence. Assume the variable is normally 9, Automobile Repairs The standard deviation of a sample of 15 automobile repairs at a local garage was $120.82. Assume the variable is normally distributed. Find the 90% confidence of the true variance and standard deviation. distributed. 90 200 80 105 85 95 70 225 105 115 100 110 125 130 145 7-36

Answer 1

3.
0:0.05 n. 12 X X. , - *.05.17 (4.575) View On : F 19.695 0 x : 0.10, n=20 L=dest, R= right- X X,19 = 1.650 X = , 19 = 127.204 127.204 2=0.05, n=27 x = x6.05.26 = 15.379 x = 0,95,26 = [38.885 o x=0.01, n=6 x = xel, 5= 10.554;Z=20.005 =15.086

@ <= 0.1, 41 * = x.1, 40 = 29,051 Na = kag, 40 = 151.805 those you can also use Excel tub XL = CHISQ. INVIQ, n-1) Xxx = CHISQ.INV (1-2, 6-1)