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A set of 200 score is normally distributed with a mean of 60 and a standard deviation of 12 . What are the z scores corresponding to the raw scores of 76,38,and 50?
Suppose a random variable X has density f(x) = c x 3; if x equal or great than 1 0; else ; where c is a constant. What is the cumulative distribution function, FX(x)?
What critical value t* from Table C would you use for a confidence interval for the mean of the population in each of the following situations?
If the no. of people working is 2 standard deviations above the mean, how many standard deviations above or below the mean you expect sales to be? What value of sales does the correspond to?
How large a sample should be taken to estimate the true mean coverage of all 1-gallon cans to within (plus/minus) 5 square feet with 95% confidence?
The time to failure of a battery in hours of a personal handheld music device follows an exponential distribution. The expected battery life is 2000 hours. Calculate the cumulative density function,
The probability of a manufacturing defect in an aluminum beverage can is .00009. If 100,700 cans are produced, find the following probabilities.
Suppose thw weekly amount spent on repairs at a certain computer is normally distributed with a mean of $300 and a standard deviation $20
A population is estimated to have a standard deviation of 16. We want to estimate the population mean within 3, with a 90 percent level of confidence. How large a sample is required? (Round up your
In their October 2003 issue, Consumer Reports evaluated the price and performance of 23 models of cordless phones. Computer output gives these summaries for the prices: Min Q1 Median Q3 Max Mean SD
Scores on a test have a mean of 71 and the score of 80 falls at the 75th percentile. The scores have a distribution that is approximately normal. Find the score that falls at the 39th percentile. pl
The estimate of the population proportion is to be within plus or minus .04, with a 98 percent level of confidence. The best estimate of the population proportion is .25. How large a sample is requi
A company studying the productivity of their employees on a new information system was interested in determining if the age (x) of data entry operators influenced the number of completed entries mad
For example, the probability that the economy will be in "boom" state is 0.15. In this case, if you invest in the stock market your return is assumed to be 25%; on the other hand if you invest in go
A medical researcher wishes to determine the percentage of females who take vitamins. He wishes to be 95% confident that the estimate is within 2.5 percentage points of the true proportion. A recent
Wildlife biologists are attempting to track the prevalence of rabies in Texas coyota populations. They trap and test coyotes in three widely separated counties to determine whether the prevalence, t
A researcher is interested in estimating the percentage of US residents without health insurance. How large a sample is needed so that the maximum margin of error of a 95% confidence interval is no
It is believed 30% of all adults are overweight. How larger sample is necessary to estimate the true proportion of adults who are overweight with a 95% confidence interval so that the margin of erro
A blood test indicates the presence of a particulat disease 95% of the time when the disease is actually present. The same test indicates the presence of the disease 0.5% of the time when the dsease
A poll of 200 American adults showed that 144 though that chemical dumps are among the most serious environmental problems. Estimate with a 98% confidence interval the proportion of the population w
The mean and standard deviation of a random sample of size 20 trees are 30.2 feet and 4.3 feet, respectively. Find the 98% confidence interval for the mean height of trees in the forest. Give a verb
Find the t-critical value for given confidence level and the sample size.
A sample has a mean of 120 and a standard deviation of 20.0. Find the value x that corresponds to each of these standard scores. Use the following formula:
Assume the population standard deviation is 2.1 pounds. b. Physician thinks that the margin of error is too large. Estimate the sample size required to estimate the mean birth weight within 0.3 poun
A researcher is interested in estimating the mean length of walleye in a lake with a 95% confidence interval. Assuming the standard deviation of lengths is inches, estimate the sample size required