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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