Posted: September 16th, 2017
Three STATS Questions Set
1. In a certain region of the country, average radar echo duration of lightning flashes is .61 sec and a standard deviation of .24 sec. Note, that these are population values. Calculate a 95% (two sided) confidence interval for the true average echo duration ? , for a random sample of 100 lightening flashes.
2. . A. What is the probability of discovering that your five best friends all have cellphone numbers ending in 7?
(Hint: first determine the probability of a single telephone number ending with a 7. Then calculate for five independent occurrences.)
& If you make a new friend tomorrow, what are the odds she will also have a cellphone number ending in 7?
(Hint: first determine the probability of a single telephone number ending with a 7. Then calculate for five independent occurrences.)
& If you make a new friend tomorrow, what are the odds she will also have a cellphone number ending in 7?
3. Most water treatment facilities monitor the quality of their drinking water on an hourly basis. One variable monitored is pH, which measures the degree of alkalinity or acidity in the water. A target pH level is 8.5. pH values below 8.5 is acidic and above 8.5 is alkaline, both of which are bad for health. A random sample of 20 measurements resulted in an average pH of 8.55 with a standard deviation of 0.28 (10 pts)
a. Does the sample provide sufficient evidence that the mean pH level in the water differs from 8.5? Conduct a test at the ? = .01 level
b. What are the upper and lower limits of the 95% confidence intervals
a. Does the sample provide sufficient evidence that the mean pH level in the water differs from 8.5? Conduct a test at the ? = .01 level
b. What are the upper and lower limits of the 95% confidence intervals
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