Question

1) Suppose the heights of 18-year-old men are approximately normally distributed, with mean 71 inches and standard deviation 5 inches.
a)
What is the probability that an 18-year-old man selected at random is between 70 and 72 inches tall? (Round your answer to four decimal places.)
b)
If a random sample of twenty-six 18-year-old men is selected, what is the probability that the mean height x is between 70 and 72 inches? (Round your answer to four decimal places.)
c)
Compare your answers to parts (a) and (b). Is the probability in part (b) much higher? Why would you expect this?
!) The probability in part (b) is much higher because the mean is larger for the x distribution.
!!) The probability in part (b) is much lower because the standard deviation is smaller for the x distribution.
!!!) The probability in part (b) is much higher because the standard deviation is smaller for the x distribution.
!!!!) The probability in part (b) is much higher because the mean is smaller for the x distribution.
!!!!!) The probability in part (b) is much higher because the standard deviation is larger for the x distribution.
2) Let x be a random variable that represents the level of glucose in the blood (milligrams per deciliter of blood) after a 12 hour fast. Assume that for people under 50 years old, x has a distribution that is approximately normal, with mean = 66 and estimated standard deviation = 45. A test result x < 40 is an indication of severe excess insulin, and medication is usually prescribed.
a)
What is the probability that, on a single test, x < 40? (Round your answer to four decimal places.)
b)
Suppose a doctor uses the average x for two tests taken about a week apart. What can we say about the probability distribution of x? Hint: See Theorem 6.1.
!) The probability distribution of x is approximately normal with x = 66 and x = 45.
!!) The probability distribution of x is approximately normal with x = 66 and x = 22.50.
!!!) The probability distribution of x is approximately normal with x = 66 and x = 31.82.
!!!!) The probability distribution of x is not normal.

c) What is the probability that x < 40? (Round your answer to four decimal places.)
d) Repeat part (b) for n = 3 tests taken a week apart. (Round your answer to four decimal places.)
e) Repeat part (b) for n = 5 tests taken a week apart. (Round your answer to four decimal places.)
f) Compare your answers to parts (a), (b), (c), and (d). Did the probabilities decrease as n increased?
Yes
NO
g) Explain what this might imply if you were a doctor or a nurse.
!) The more tests a patient completes, the weaker is the evidence for lack of insulin.
!!) The more tests a patient completes, the stronger is the evidence for lack of insulin.
!!!) The more tests a patient completes, the weaker is the evidence for excess insulin.
!!!!) The more tests a patient completes, the stronger is the evidence for excess insulin.

Answer 1

Answer:

Suppose the heights of 18-year-old men are approximately normally distributed, with mean 71 inches and standard deviation 4 inches.

(a) What is the probability that an 18-year-old man selected at random is between 70 and 72 inches tall? (Round your answer to four decimal places.)

z1 = (70-71)/4 = -0.25

z2 = (72-71/4 = 0.25

P(70<X<72) = p(-0.25<z<0.25) = 0.1974

Answer: 0.1974

(b) If a random sample of thirteen 18-year-old men is selected, what is the probability that the mean height x is between 70 and 72 inches? (Round your answer to four decimal places.)

z1 = (70-71)/(4/sqrt(13)) = -0.9014

z2 = (72-71/(4/sqrt(13)) = 0.9014

P(70<X<72) = p(-0.9014<z<0.9014) = 0.6326

Answer: 0.6326

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