In: Statistics and Probability
5. The average age of a vehicle registered in the United States is 8 years, or 96 months. If a random sample of 36 vehicles is selected, find the probability that the mean of their age is between 98 and 100 months? Assume the standard deviation for the population is 15.
Solution :
Given that ,
mean = = 96
standard deviation = = 15
n = 36
= 96
= / n= 15/ 36=2.5
P(98< < 100) = P[(98-96) / 2.5< ( - ) / < (100-96) /2.5 )]
= P( 0.8< Z <1.6 )
= P(Z <1.6 ) - P(Z < 0.8)
Using z table
=0.9452-0.7881
=0.1571
probability= 0.1571