Review from before Christmas Break

Sampling Distributions

Properties of a sampling distribution of means:

Sampling Distributions

Properties of a sampling distribution of proportions:

About 13% of the population is left-handed. What’s the probability that less than 10% of a class of 50 is left-handed?

The mean adult weight is 175 pounds with a standard deviation of 25 pounds. Assumption of normal is appropriate. What is the probability that I randomly choose a person who is more than 200 pounds?

The mean score on a standardized test is 120 with a standard deviation of 15 points. What’s the probability that a group of 40 people will have a mean score of at least 128.

Approximately 28% of the population would like a new house. What’s the probability that at most 40 out of 150 people interviewed will want a new house.

In May 2002, the Gallup Poll asked 537 randomly sampled adults the question, “Do you believe the death penalty is applied fairly or unfairly in this country today”. Of these, 53% said “fairly”. Find a 90% confidence interval for the proportion of US adults who agree.

Suppose a simple random sample of 150 students is drawn from a population of 3000 college students. Among sampled students, the average IQ score is 115 with a standard deviation of 10. What is the 99% confidence interval for student’s IQ scores?

What happens to the interval if I go from a 92% confidence interval to a 99% interval using the same sample size?

If I keep the same confidence level (92%), but increase the sample size by 100, what will happen to the interval?

Explain what a 90% confidence interval is.

Explain what a 90% confidence level is.

Standard Error

It’s the estimated standard deviation of the statistic

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