posted by Liza .
a manufacturing plant uses 3000 light bulbs whose lifetimes are independently normally distributed with mean 500 hrs, and standard deviation 50 hrs. to minimize the number of bulbs that burn out during production hours, all bulbs are replaced after given period of operation. how often should the bulbs be replaced if you want no more than 1% to burn out between replacements?
Should I just look up 1% under the z-distribution and find corresponding z-score to it, and with that find the X-value in hours?