In a test on 2000 electric bulbs it was found that the life of a particular make was normally distributed with an average life of 2040 hours and Standard deviation of 60hours Estimate the number of bulbs likely to burn for

7 c] In a test on 2000 electric bulbs, it was found that the life of a particular make was
normally distributed with an average life of 2040 hours and Standard deviation of 60
hours. Estimate the number of bulbs likely to burn for
i. More than 2150 hours
ii. Less than 1950 hours
iii. Between 1920 and 2160 hours