The Local authorities in a certain city install 10,000 electric lamps in the street of the city., f
these lamps have an average life of 1,000 burning hours with a standard deviation of 200 hours,
assuming normality, what number of lamps might be expected to fail
In the first 800 burning hours.
1) Between 800 and 1,200 burning hours.
After what period of burning hours would you expect that
10% of the lamp would fail?
10% of the lamps would be still burning?