The average noise level in a diner is 30 decibels with a standard deviation of 6 decibels. ninety-nine percent of the time, the noise level is below what value?
Assuming a normal distribution the noise level is below 44dB 90% of the time.
Looking up the standard deviation that goes along with .01 on a normal distribution chart, we find that 2.33 standard deviations is the answer. Given the standard deviation of six we turn this in to deviation in decibels from the mean:
6*2.33 = 13.98
Add this to the mean to get
30+13.98=43.98
which we round to 44dB
