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Name: __________________________________________________ Date: _____________________________ Period: ___________________Practice: Critical ValuesExplain when a t statistic is used rather than a z-score. Provide two reasons.Using the t-tables, software, or calculator, estimate…The critical value of t for a 90% confidence interval with df = 17The critical value of t for a 98% confidence interval with df = 88.The P-value for t≥2.09 with 4 degrees of freedomThe P value for t>1.78 with 22 degrees of freedomThe critical value for t for a 95% confidence interval with df = 7The critical value for t for a 99% confidence interval with df = 102The P-value for t≥2.19 with 41 degrees of freedomThe P value for t>2.33 with 12 degrees of freedomThe weight of potato chips in a medium-size bag is stated to be 10 ounces. The amount that the packaging machines puts in these bags in believed to have a Normal model with a mean of 10.2 ounces and a standard deviation of 0.12 ounces. (OLD MATERIAL)Why can you use a z-test statistic in this example?What fraction of all bags are underweight?Some of the chips are sold in “bargain packs” of 3 bags. What’s the probability that none of the 3 is underweight?What’s the probability that the mean weight of the 3 bags is below the stated amount?What’s the probability that the mean weight of a 24-bag case of potato chips is below 10 ounces? Acme Corporation manufactures light bulbs. The CEO claims that an average Acme light bulb lasts 300 days. A researcher randomly selects 15 bulbs for testing. The sampled bulbs last an average of 290 days, with a standard deviation of 50 days. If the CEO's claim were true, what is the probability that 15 randomly selected bulbs would have an average life of no more than 290 days?Suppose scores on an IQ test are normally distributed, with a population mean of 100. Suppose 20 people are randomly selected and tested. The standard deviation in the sample group is 15. What is the probability that the average test score in the sample group will be at most 110?Multiple Choice:One reason for using the t-distribution instead of the standard Normal curve to find the critical values when calculating a confidence interval for a population mean is that…z can only be used for large samplesz requires that you know the population standard deviation σz requires that you can regard your data as an SRS from the populationyou can’t find confidence intervals using z-test statistics.A z critical value will lead you to a wider interval than a t critical valueYou have an SRS of 23 observations from a Normally distribution population. What critical value would you use to obtain a 98% confidence interval for the mean of the population if the standard deviation is unknown?2.5082.3262.1772.5002.183 ................
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