The fluorescent light tubes made by the company Well-lit have lifetimes which are
normally distributed with mean 2019 hours and standard deviation 20 hours. The
company decides to promote its sales of the tubes by guaranteeing a minimum life of
the tubes, replacing free of charge any tubes that fail to meet this minimum life. If the
company wishes to replace only 3% of the tubes sold, find the guaranteed minimum
it must set.

Question

The fluorescent light tubes made by the company Well-lit have lifetimes which are 
normally distributed with mean 2019 hours and standard deviation 20 hours. The 
company decides to promote its sales of the tubes by guaranteeing a minimum life of 
the tubes, replacing free of charge any tubes that fail to meet this minimum life. If the 
company wishes to replace only 3% of the tubes sold, find the guaranteed minimum 
it must set.