
Concept explainers
Blood pressure: High blood pressure has been identified as a risk factor for heart attacks and strokes. The National Health and Nutrition Examination Survey reported that the proportion of U.S. adults with high blood pressure is 0.3. A sample of 38 U.S. adults is chosen.
- Is it appropriate to use the normal approximation to find the
probability that more than 40% of the people in the sample have high blood pressure? If so, find the probability. If not; explain why not. - A new sample of 80 adults is drawn. Find the probability that more than 40% of the people in this sample have high blood pressure.
- Find the probability that the proportion of individuals in the sample of 80 who have high blood pressure is between 0.20 and 0.35.
- Find the probability that less than 25% of the people in the sample of 80 have high blood.
- Would it be unusual if more than 45% of the individuals in the sample of 80 had high blood pressure?
a.

Whether it is appropriate to use the normal approximation to find the probability that more than 40% of the people in the sample have high blood pressure under given scenario.
Answer to Problem 22E
The probability that more than 40% of the people in the sample have high blood pressure.
is 0.0764 .
Explanation of Solution
Given Information:
The National Health and Nutrition Examination Survey reported that the proportion of U.S. adults with high blood pressure is 0.3. A sample of 38 U.S. adults is chosen.
Formula used:
The standard deviation is
σP=√p(1−p)n
where n is sample size and p is population proportion.
Calculation:
Given that the sample size is n=38 and population proportion is p=0.3 .
Since, np=(38)(0.3)=11.4≥10
And n(1−p)=(38)(1−0.3)=26.6≥10 .
This means normal approximation can be used to find the probability that more than 40% of the people in the sample have high blood pressure.
The mean is μp=p=0.3
The standard deviation is,
σp=√p(1−p)n=√0.3(1−0.3)38=0.07
Calculating the z score for 0.40 as below,
z=ˆp−μpσp=0.40−0.30.07=1.43
The required probability is
P(ˆp>0.40)=1−P(ˆp<0.40)=1−P(z<1.43)=1−0.9236=0.0764
Hence, the probability that more than 40% of the people in the sample have high blood pressure.
is 0.0764 .
b.

The probability of more than 40% of the people in the sample of 80 adults having high blood pressure.
Answer to Problem 22E
The probability that more than 40% of the people in the sample of 80 adults have high blood pressure is 0.0228 .
Explanation of Solution
Given Information:
∧p=0.4n=80p=0.3
Formula used:
σˆp=√p(1−p)n
Calculation:
Given that the sample size is n=80 and population proportion is p=0.4 .
Since, np=(80)(0.4)=32≥10
And n(1−p)=(80)(1−0.4)=48≥10 .
This means normal approximation can be used to find the probability that more than 40% of the people in the sample have high blood pressure.
Now mean is μp=p=0.3
The standard deviation is,
σp=√p(1−p)n=√0.3(1−0.3)80=0.05
Calculating the z score for 0.40 as below,
z=ˆp−μpσp=0.40−0.30.05=2
The required probability will be given as,
P(ˆp>0.40)=1−P(ˆp<0.40)=1−P(z<2)=1−0.9772=0.0228
Hence, the probability that more than 40% of the people in the sample of 80 adults have high blood pressure is 0.0228 .
c

The probability that the proportion of individuals in the sample of 80 who have high blood pressure is between 0.20 and 0.35 .
Answer to Problem 22E
The probability that the proportion of individuals in the sample of 80 who have high blood pressure is between 0.20 and 0.35 would be 0.8185 .
Explanation of Solution
Given Information:
∧p1=0.4,∧p2=0.4,n=80,μp=p=0.3,σp=0.05
Calculation:
Calculating the z score for 0.20 as below,
z=ˆp−μpσp=0.20−0.30.05=−2
Calculating the z score for 0.35 as below,
z=ˆp−μpσp=0.35−0.30.05=1
The required probability is
P(0.20<ˆp<0.35)=P(ˆp<0.35)−P(ˆp<0.20)=P(z<1)−P(z<−2)=0.8413−0.0228=0.8185
Hence, the probability that the proportion of individuals in the sample of 80 who have high blood pressure is between 0.20 and 0.35 would be 0.8185 .
d

The probability that less than 25% of the people in the sample of 80 have high blood pressure.
Answer to Problem 22E
The required answer is 0.1587
Explanation of Solution
Given Information:
∧p1=0.25,n=80,μp=p=0.3,σp=0.05
Calculation:
Calculating the z score for 0.25 as below,
z=ˆp−μpσP=0.25−0.30.05=−1
The required probability is
P(ˆp<0.25)=P(z<−1)=0.1587
Hence, the probability that less than 25% of the people in the sample of 80 have high blood pressure would be 0.1587 .
e.

If it is unusual for more than 45% of the individuals in the sample of 80 to have high blood pressure.
Answer to Problem 22E
Yes, it would be unusual if more than 45% of the individuals in the sample of 80 had a high blood pressure.
Explanation of Solution
Given Information:
∧p=0.45,μp=p=0.3,σp=0.05
Calculation:
Calculating the z score for 0.25 as below,
z=ˆp−μpσP=0.45−0.30.05=3
The required probability is.
P(ˆp<0.45)=1−P(z<3)=1−0.9987=0.0013
The above probability is very low. Hence, it would be unusual if more than 45% of the individuals in the sample of 80 had a high blood pressure.
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Chapter 7 Solutions
Elementary Statistics ( 3rd International Edition ) Isbn:9781260092561
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