SOLUTION: The average age of Amtrak passenger train cars is 19.4 years. If the distribution of ages is normal and 19% of the cars are older than 21.7 years, find the standard deviation.

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Question 1081764: The average age of Amtrak passenger train cars is 19.4 years. If the distribution of ages is normal and 19% of the cars are older than 21.7 years, find the standard deviation.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
So when p=0.81, the z score will correlate to an age of 21.7.
For p=0.81, z=0.8779
0.8879=%2821.7-19.4%29%2Fsigma
sigma=2.3%2F.8879
Work that out for the answer.