The metropolitan airport commission is considering establishment of limitations on extent of noise pollution around local airport. At the present time the noise level per jet takeoff in one neighborhood near airport is approximately normally distributed with mean of 100 decibels and standard deviation of 6 decibels.
Assume a regulation is passed which requires jet noise in this neighborhood to be lower than 105 decibels 95% of time. Supposing the standard deviation of the noise distribution remains the same, how much will the mean noise level have to be lowered to comply with regulation?