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# A RANDOM SAMPLE OF 89 OBSERVATIONS PRODUCED A MEAN X (X BAR) = 25.8 AND A STANDARD DEVIATION S= 2.4.

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Author: Christine Farr
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A random sample of 89 observations produced a mean x (x bar) = 25.8 and a standard deviation s= 2.4.- find a 95, 90, and 99% confidence interval for u.In a sample of 304,000 items mailed between Dec. 10 and Mar. 3, the accounting firm determined that 268,100 items were delivered on time. Assuming a confidence level of 95%, the likelihood of an item being delivered on time is in the interval __ , __.The mean gas mileage for a hybrid car is 56 miles per gallon (MPG). Suppose that the gas mileage is approximately normally distributed with a standard deviation of 3.3 MPG. a. The probability that a randomly selected hybrid gets more than 62 MPG is __?b. The probability that a randomly selected hybrid gets 50 MPG or less is __?c. The probability that a randomly selected hybrid gets between 57 and 62 MPG is __?d. The probability that a randomly selected hybrid gets less than 46 MPG is __?The random sample shown below was selected from a normal distribution. 9, 3, 7, 3, 9, 5.a. construct a 95% confidence interval for the population mean u __ , __.b. assume that sample mean x (x bar) and sample standard deviation s remains exactly the same as those you just calculated but that are based on a sample of n=25 observations. Repeat part a. what is the effect of increasing the sample size on the width of the confidence intervals? The confidence interval is __ , __? What is the effect of the sample size on the width of the confidence interval? As the sample size increases, the width increases, stays same or decreases?

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