Question

The ideal (daytime) noise-level for hospitals is 45 decibels with a standard deviation of 12 db; which is to say, this may not be true. A simple random sample of 70 hospitals at a moment during the day gives a mean noise level of 47 db. Assume that the standard deviation of noise level for all hospitals is really 12 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)

(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 (42.28db, ___ 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?

Answer 1