A manufacturing plant utilizes 3000 electric light bulbs whose length of life is normally distributed with mean 500 hours and standard deviation 50 hours. To minimize the number of bulbs that burn out...

Statistics and Probability Question

Extracted text: A manufacturing plant utilizes 3000 electric light bulbs whose length of life is normally distributed with mean 500 hours and standard deviation 50 hours. To minimize the number of bulbs that burn out during operating hours, all the bulbs are replaced after a given period of operation. How often should the bulbs be repladed if we want not more than 1% of the bulbs to burn out between replacement periods? (use comma please)