In: Math
(THE PROBABILITIES ABOUT X) : Set up and ind the indicated probability; a diagram is recommended.
4.) The average age of a vehicle registered in the United States is 8 years, or 96 months. Assume the standard deviation is 16 months. If a random sample of 36 vehicles is selected, ind the probability that the mean of their age is between 90 and 100 months.
Solution :
Given that,
mean =
= 96
standard deviation =
= 16
n=36
= 96
=
/
n = 16 /
36=2.67
= P(90<
< 100) = P[(90-96) / 2.67< (
-
) /
< (100-96) / 2.67)]
= P( -2.25< Z <1.50 )
= P(Z <1.50 ) - P(Z < -2.25)
Using z table,
= 0.9332-0.0122
probability = 0.9210