# Good practice of statistics...could you like to help me?

**Question description**

The mean time before failure of the integrated circuits for a simple random sample of 25 calculators, with a sample mean time of 112 hours, a known standard deviation of 18 hours, but the distribution is exponential.

- In a study to test the effectiveness of nutritional supplements on respiratory tract infections, 337 children were given supplements and 370 were given a placebo. The days of peak severity in the treatment group had a mean of 6.0 days and a standard deviation 2.3 days. The placebo group had a mean of 6.1 days and a standard deviation 2.4 days.

a) What is the 95% confidence interval for the mean number of days for the treatment group?

b) What is the 95% confidence interval for the mean number of days for the placebo group?

c) What does the study suggest about the effectiveness of nutritional supplements?

4. Mayor Fastbuck has 51% of the vote after 1000 randomly-selected ballots have been counted. With a 99% confidence, do you think Fastbuck has stolen won another term as mayor?

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