The distribution for the working life tike of light bulbs manufactured in a company,is found to be normally distributed with a mean of 1450 hours and a standard deviation of 60 hours. IN this distribution find the life time of a lightbulb whose z-score is -1.8. The distribution for the working life tike of light bulbs manufactured in a company,is found to be normally distributed with a mean of 1450 hours and a standard deviation of 60 hours. IN this distribution find the life time of a lightbulb whose z-score is -1.8