The lifetime of lightbulbs that are advertised to last for 6

The lifetime of lightbulbs that are advertised to last for 6000 hours are normally distributed with a mean of 6250 hours and a standard deviation of 100 hours. What is the probability that a bulb lasts longer than the advertised figure? Use Excel to obtain more accuracy. Probability =

Solution

Normal Distribution
Mean ( u ) =6250
Standard Deviation ( sd )=100
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
P(X > 6000) = (6000-6250)/100
= -250/100 = -2.5
= P ( Z >-2.5) From Standard Normal Table
= 0.9938