# mathematics

The ideal (daytime) noise-level for hospitals is 45 decibels with a standard deviation of 10 db. A simple random sample of 81 hospitals at a moment during the day gives a mean noise level of 47 db. Assume that the standard deviation of noise level is really 10 db. All answers to two places after the decimal. (a) A 99% confidence interval for the actual mean noise level in hospitals is(______db , ______db) (b) We can be 90% confident that the actual mean noise level in hospitals is______db with a margin of error of______db. (c) Unless our sample (of 81 hospitals) is among the most unusual 2% of samples, the actual mean noise level in hospitals is between______db and ______db. (d) A 99.9% confidence interval for the actual mean noise level in hospitals is (______db, ______db). (e) Assuming our sample of hospitals is among the most typical half of such samples, the actual mean noise level in hospitals is between______db and ______db. (f) We are 95% confident that the actual mean noise level in hospitals is______db,  with a margin of error of______db. (g) How many hospitals must we examine to have 95% confidence that we have the margin of error to within 1 db? ______. (h) How many hospitals must we examine to have 99.9% confidence that we have the margin of error to within 1 db? ______.

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