Answer: (a) Percentage of 25 year old men that are above 6 feet 2 inches is 11.5%.
(b) Percentage of 25 year old men in the 6 footer club that are above 6 feet 5 inches are 2.4%.
Step-by-step explanation:
Given that,
Height (in inches) of a 25 year old man is a normal random variable with mean
and variance
.
To find: (a) What percentage of 25 year old men are 6 feet, 2 inches tall
(b) What percentage of 25 year old men in the 6 footer club are over 6 feet. 5 inches.
Now,
(a) To calculate the percentage of men, we have to calculate the probability
P[Height of a 25 year old man is over 6 feet 2 inches]= P[X>
]
P[X>74] = P[
>
]
= P[Z > 1.2]
= 1 - P[Z ≤ 1.2]
= 1 - Ф (1.2)
= 1 - 0.8849
= 0.1151
Thus, percentage of 25 year old men that are above 6 feet 2 inches is 11.5%.
(b) P[Height of 25 year old man is above 6 feet 5 inches gives that he is above 6 feet] = P[X,
- X,
]
P[X >
I X >
] = P[X > 77 I X > 72]
= ![\frac{P[X > 77]}{P[ X > 72]}](https://tex.z-dn.net/?f=%5Cfrac%7BP%5BX%20%3E%2077%5D%7D%7BP%5B%20X%20%3E%2072%5D%7D)
= ![\frac{P[\frac{X - g}{o}>\frac{77-71}{2.5}] }{P[\frac{X-g}{o} >\frac{72-71}{2.5}] }](https://tex.z-dn.net/?f=%5Cfrac%7BP%5B%5Cfrac%7BX%20-%20g%7D%7Bo%7D%3E%5Cfrac%7B77-71%7D%7B2.5%7D%5D%20%20%7D%7BP%5B%5Cfrac%7BX-g%7D%7Bo%7D%20%3E%5Cfrac%7B72-71%7D%7B2.5%7D%5D%20%7D)
= ![\frac{P[Z >2.4]}{P[Z>0.4]}](https://tex.z-dn.net/?f=%5Cfrac%7BP%5BZ%20%3E2.4%5D%7D%7BP%5BZ%3E0.4%5D%7D)
= ![\frac{1-P[Z\leq2.4] }{1-P[Z\leq0.4] }](https://tex.z-dn.net/?f=%5Cfrac%7B1-P%5BZ%5Cleq2.4%5D%20%7D%7B1-P%5BZ%5Cleq0.4%5D%20%7D)
= 
= 
= 0.024
Thus, Percentage of 25 year old men in the 6 footer club that are above 6 feet 5 inches are 2.4%.