Question

The ages of commercial aircraft are normally distributed with a mean of 13.5 years and a standard deviation of 7.2 years. What percentage of individual aircraft have ages greater than 15 years? Assume that a random sample of 81 aircraft is selected and the mean age of the sample is computed. What percentage of sample means have ages greater than 15 years? The percentage of individual aircraft that have ages greater than 15 years is nothing%. (Round to the nearest integer as needed.) The percentage of sample means that have ages greater than 15 years is nothing%. (Round to the nearest integer as needed.)

Answer #1

(A) use normalcdf(lower, upper, mean, standard deviation)

we have lower = 15, upper = 1E99, mean = 13.5 and standard deviation = 7.2

P(X>15) = normalcdf(15,1E99,13.5,7.2) = 0.4175

P(X>15) = 42% (rounded)

(B) use normalcdf(lower, upper, mean, standard deviation)

we have lower = 15, upper = 1E99, mean = 13.5 and standard deviation =

P(>15) = normalcdf(15,1E99,13.5,0.8) = 0.0304

P(>15) = 3% (rounded)

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Selected Answer 0.9599 was WRONG

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