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)