SOLUTION: The average age of Amtrak passenger train cars is 19.4 years. If the distribution of ages is normal and 20% of the cars are older than 22.8 years, find the standard deviation.

Algebra ->  Algebra  -> Probability-and-statistics -> SOLUTION: The average age of Amtrak passenger train cars is 19.4 years. If the distribution of ages is normal and 20% of the cars are older than 22.8 years, find the standard deviation.      Log On

Ad: Algebra Solved!™: algebra software solves algebra homework problems with step-by-step help!
Ad: Algebrator™ solves your algebra problems and provides step-by-step explanations!

   

Question 133640This question is from textbook Statistics
: The average age of Amtrak passenger train cars is 19.4 years. If the distribution of ages is normal and 20% of the cars are older than 22.8 years, find the standard deviation.This question is from textbook Statistics

Answer by stanbon(48568) About Me  (Show Source):
You can put this solution on YOUR website!
The average age of Amtrak passenger train cars is 19.4 years. If the distribution of ages is normal and 20% of the cars are older than 22.8 years, find the standard deviation.
-------------------------------
mu = 19.4
Find the z-value associated with upper 20%:
InvNorm(0.80) = 0.8416
Use z = (x-mu)/sigma to find sigma
0.8416 = (22.8-19.4)/sigma
sigma = (22.8-19.4)/0.8416
sigma = (3.4)/0.8416 = 4.0399
==================================
Cheers,
Stan H.