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Sample Sizes
Interval Length & Critical Values
1 Sample Confidence Interval
1 and 2 Sample Confidence Intervals
Random
100
When doing a confindence interval for difference of means, and the sample size for the populations is less than 30 what critical value do you use?
tc
100
What happens to the width of the intervals when you increase your confidence level?
they get wider or longer
100
For a one sample proportion confidence interval the middle value of the interval is equal to what?
p
100
2 Sample Confidence Interval for proportions compares what two values?
p1 and p2
100
What was the score of this year's Super Bowl?
21-17
200
When can we use n = p(1-p)(Zc/E)^2 to find sample size?
When we have a prelim. estimate for p.
200
What happens to the width of the intervals when you increase E?
wider
200
What is the formula for a 1 sample p confidence interval?
p-hat plus or minus E
200
The average heights of a random sample of 400 people from a city is 1.75 meters with a standard deviation of 0.4 meters. The average heights of a second random sample of 500 people from a city is 1.82 meters with a standard deviation of 0.5 meters. Compute a confidence interval of 90%, for the difference of the two means.
-.012 to -.02
200
What year was the Declaration of Independence signed?
1776
300
The average heights of a random sample of 400 people from a city is 1.75 meters. It is known that the heights of the population are random variables that follow a normal distribution with a standard deviation of 0.4 meters. With a confidence level of 90%, what would the minimum sample size need to be in order for the true mean of the heights to be within .02 m from the sample mean?
1083
300
For a sample Size of 20. What are the degrees of freedom?
19
300
What does n*p-hat and n*q-hat have to be greater than?
5
300
The average heights of a random sample of 400 people from a city is 1.75 m. It is known that the heights of the population are random variables that follow a normal distribution with a standard deviation of 0.4 m. Determine the interval of 95% confidence for the average heights of the population.
n = 400 x = 1.75 σ = 0.4 c = 0.95 zc = 1.96 (1.75 ± 1.96 · 0.4/20 ) → (1.7108,1.7892)
300
What was the first name of the President of the United States more commonly known as FDR?
Franklin
400
What sample size should be taken to estimate p within .05 at a 95% level?
385
400
For 2 samples, one of Size of 11 and one of size 13, what are the degrees of freedom? and the corresponding Tc for a 85% level?
22 and 1.492
400
Which of the following statements is true. I. The margin error (E) is computed solely from sample attributes and a critical value II. The sample standard deviation is x-bar. III. The standard deviation is a measure of central tendency. (A) I only (B) II only (C) III only (D) All of the above. (E) None of the above.
The correct answer is (A)
400
What happens to the width of the intervals when you increase your sample size?
The intervals become narrower
400
What is the next prime number after 19?
23
500
From previos studies pro football players weights have shown a standard deviation of 20 lbs. To ensure a confidence level of 90%, what would the minimum sample size need to be in order for the true mean of weights to be within 2 lbs. from the sample mean?
271
500
2 samples are taken, one of Size of 11 and one of size 13. The first has a mean of 6 and st. dev. of 1. The second has a mean of 4 and a st. dev. of 0.95. What is the pooled standard deviation (rounded to the thousandths)?
0.973
500
Suppose we want to estimate the average weight of an adult male in Dekalb County, Georgia. We draw a random sample of 1,000 men from a population of 1,000,000 men and weigh them. We find that the average man in our sample weighs 180 pounds, and the standard deviation of the sample is 30 pounds. What is the 95% confidence interval. (A) 180 +- 1.86 (B) 180 +- 3.0 (C) 180 +- 5.88 (D) 180 +- 30 (E) None of the above
The correct answer is (A)
500
Suppose that you want to find out the average weight of all players on the football team at Landers College. You are able to select ten players at random and weigh them. The mean weight of the sample of players is 198, so that number is your mean estimate. The population standard deviation is σ = 11.50. What is a 90 percent confidence interval for the population weight, if you presume the players' weights are normally distributed?
You are 90 percent certain that the true population mean of football player weights is between 192 and 204 pounds.
500
What is the Greatest common factor of 68 and 119?
17