Suppose that on average electricians earn approximately 540

Suppose that, on average electricians earn approximately $ 54,000 per year in the U.S. Assume that the distribution for electrician’s yearly earnings is normally distributed and that the standard deviation is $ 12,000. What is the probability that the average salary of four randomly selected electricians exceeds $ 60,000?

0.1587

0.3085

0.6915

0.8413

Solution

Normal Distribution
Mean ( u ) =54000
Standard Deviation ( sd )=12000
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
P(X > 60000) = (60000-54000)/12000
= 6000/12000 = 0.5
= P ( Z >0.5) From Standard Normal Table
= 0.3085