# confsumhandout - Confidence intervals scenarios and data 1...

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Confidence intervals: scenarios and data 1. σ known A candle making process is known to produce candles whose life times have a variance of 0.4 hours. However, the average lifetime is un- known. The lifetimes of a random sample of six candles turned out to be 8.1, 8.7,9.2,7.8,8.4,9.4 hours respectively. Find a 99% confidence interval for the population mean. 2. σ unknown, n small, non-Normal An experiment was performed to de- termine whether two different forms of iron (Fe 2+ and Fe 3+ ) are retained dif- ferently in the body. If one form were retained better, it would be the better dietary supplement. The investigators divided 36 mice randomly into two groups of 18 each; one group was given Fe 2+ and the other Fe 3+ at the same concentration. The iron was administered orally; it was radioactively labelled so that a radiation counter could measure the amount administered and the amount retained after a fixed amount of time had elapsed. The percentage of iron retained is listed for each mouse below. Obtain a 95% confidence interval

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