Answer to Question #46079 in Statistics and Probability for stilla

Question

In a test on 2500 electric bulbs, it was found that the life of a particular make was normally distributed with an average life of 2000 hours and S. D. of 60 hours. Estimate the number of bulbs likely to burn for (i) more than 2100 hours, (ii) less than 1950 hours and (iii) more than 1900 hours and but less than 2100 hours.