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1. Younger people use their cell phones to text more often than older people. A random sample of 625 teens aged 12 to 17 who use their cell phones to text found that 475 sent more than 10 text messages in a typical day. In a random sample of 1917 adults aged 18 and over who use their cell phones to text, 786 sent more than 10 text messages a day. (A) What is the standard error (SE) of the sample estimate of p1 - p2 (where p1 is the proportion for teens aged 12 to 17 and p2 is the proportion for adults 18 and older) ? (B) Give a 90% confidence interval for p1 - p2 (where p1 is the proportion for teens aged 12 to 17 and p2 is the proportion for adults 18 and older)? 2. Consider a sample of 148 small businesses. During a three-year period, 15 of 106 headed by men and 7 of the 42 headed by women failed. Let p1 be the proportion of businesses headed by women that failed. Let p2 be the proportion of businesses headed by men that failed. (A) Find the pooled proportion of businesses that failed. (B) Find the test statistic for a significance test to see if this is evidence the proportion of businesses failed is higher for women than for men. 3. We have two samples. The first sample taken in Alaska in 1999 involved 2100 adults, of which 600 were current smokers. The second sample taken in Alaska in 2009 involved 2400 adults, of which 500 were smokers. The samples are to be compared to determine if the proportion of adults in Alaska who smoke has decreased since 1999. Take p1 to be the proportion of smokers in the 1999 sample, and p2 to be the proportion of smokers in the 2009 sample. (A) What is the pooled sample estimate of adult smokers in Alaska? (B) What is the z test statistic for comparing the proportions of smokers in Alaska in 1999 and 2009? (C) Is there good evidence that the proportion of smokers has decreased over these 10 years? (D) What is the Margin of error for the 90% (large-sample) confidence interval for p1-p2? Note: We do not do plus-four confidence intervals.
Suppose that 15% of the population is left-handed. If 20 people are selected at random, find the probability that exactly 4 of them are left-handed.
Construct a graph of the probability distribution of X. What is the probability that a child receives exactly three diagnostic services during and office visit to a pediatric specialist?
Cars arrive at a toll booth at a mean rate of five cars every 10 minutes according to a Poisson process. Find the probability that the toll collector will have to wait longer than 26.30 minutes before collecting the eighth toll.
The shelf and purchases it, and he later discovers that the lamp he purchased is defective. What is the probability that the defect came with the first shipment?
Can we conclude at the 5% significance level that the population mean weight of athletic men is lower than the population mean weight of non-athletic men?
The management of a chain of fast food restaurants wants to investigate the relationship between the daily sales volume (in dollars) of a company restaurant and the number of competitor restaurants within a 1 mile radius. The following data have b..
A newspaper ad for a manager trainee position contained the statement "Our manager trainees have a first-year earnings average of $20,000 to $24,000." Do you think that the ad is describing a confidence interval? Explain your answer.
Given below is the rate of return for one year (reported in percent) for the sample of 12 mutual funds. Using .05 significance level is it sensible to conclude that mean rate of return is more than 4.50 percent?
Using the simple test of independence (described in the lecture), decide if the events high calorie and high fiber are independent or dependent. Show your work.
A -0.947 correlation coefficient has been found between two variables after examining 43 pairs of observations. What can be concluded?
In your organization's management development program, there was a heated discussion between people who claimed that theory is impractical and not effective
Identify the point estimate of the average number of available hotel rooms in this lesson from each sample. Construct and Interpret a 95% confidence level for the true mean number of available hotel rooms, based on the point estimate of each sampl..
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