Practice Problems: Confidence Intervals Answer A university wants to know more about the knowledge of students regarding international events. According to a survey, the average British household is expected to spend £868 on holiday-related expenses during the Christmas period 2013. You can assume a normal distribution because of the large sample size. Viewed 244 times 1 $\begingroup$ Question: The mean lifetime expected from a model of automobile follows a normal distribution with a standard deviation of 9500km. The confidence interval is the plus-or-minus figure usually reported in newspaper or television opinion poll results.For example, if you use a confidence interval of 4 and 47% percent of your sample picks an answer you can be "sure" that if you had asked the question of the entire relevant population between 43% (47-4) and 51% (47+4) would have picked that answer. The sample standard deviation is 2.8 inches. and for part ii I tried to solve it the same way we did in class (using the confidence interval formula = p hat +/ z*SE(p hat) and got (0.0654, 0.1305) but it says. Confidence intervals are one way to represent how "good" an estimate is the larger a 90% confidence interval for a particular estimate, the more caution is required when using the estimate. To find the mean (x̄), add all of the numbers together and.
The confidence interval consists of the upper and lower bounds of the estimate you expect to find at a given level of confidence.
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