a. P(Z
b. P(Z>x)=0.0606.
c. P(0≤Z≤x)=0.4783.
d. P(−1.5≤Z≤x)=0.2313.
e. P(−x≤Z≤x)=0.5467.
12. It is known that the glucose level in blood of diabetic
persons follows a normal
distribution model with mean 106 mg/100 ml and standard deviation 8 mg/100 ml.
a. Calculate the probability of a random diabetic person having a glucose level less
than 120 mg/100 ml.
b. What percentage of persons have a glucose level between 90 and 120 mg/100
ml?
13. It is known that the cholesterol level in males 30 years old follows a normal
distribution with mean 220 mg/dl and standard deviation 30 mg/dl. If there are
20000 males 30 years
old in the population,
a. How many of them have a cholesterol level between 210 and 240 mg/dl?
b. If a cholesterol level greater than 250 mg/dl can provoke a thrombosis, how
many of them are at risk of thrombosis?
c. Calculate the cholesterol level above which 20% of the males are?
14. In a population with 40000 persons, 2276 have between 0.8 and 0.84 milligrams of
bilirubin per deciliter of blood, and 11508 have more than 0.84. Assuming that the
level of bilirubin in blood follows
a normal distribution model,
a. Calculate the mean and the standard deviation.
b. How many persons have more than 1 mg of bilirubin per dl of blood?
15.
.
If 95% of households have a TV and 8 houses are surveyed, what is the probability
that more than 6 have a TV?
16. A manufacturer knows that an average of 1 out of 10 of his products are faulty.
What is the probability that a random sample of 5 articles will contain:
a. No
faulty products
b. Exactly 1 faulty products
c. At least 2 faulty products
d. No more than 3 faulty products
17. Complete the table for the following binomial distributions:
n
p
mean
variance
standard
deviation
a
50
0.5
b
20
5
c
0.4
100
where n = number of trials and p = probability of a success.
18.
The probability that cars passing a speed camera are speeding is 0.23. If 750 cars
pass the camera, how many of the cars would you expect to be speeding and what
would be the standard deviation?
19.
A population is known to be normally distributed with a standard deviation of 2.8.
a.
Compute the 95% confidence interval
on the mean based on the
following sample of nine: 8, 9, 10, 13, 14, 16, 17, 20, 21.
b.
Now compute the 99% confidence interval using the same data.
20. You do a study of hypnotherapy to determine how effective it is in increasing the
number of hours of sleep subjects get each night. You measure hours of sleep for 12
subjects with the following results. Construct a 95% confidence interval for the
mean number of hours slept for the population (assumed normal) from which you
took the data.
8.2; 9.1; 7.7; 8.6; 6.9; 11.2; 10.1; 9.9; 8.9; 9.2; 7.5; 10.5
21. A random sample of 20 nominally measured 2mm diameter
steel ball bearings is
taken and the diameters are measured precisely. The measurements, in mm, are as
follows: 2.02 1.94 2.09 1.95 1.98 2.00 2.03 2.04 2.08 2.07 1.99 1.96 1.99 1.95 1.99
1.99 2.03 2.05 2.01 2.03 Assuming that the diameters are normally distributed with
unknown mean, µ, and unknown variance σ 2 ,
a. Find a two-sided 95% confidence interval for the variance
b. Find a two-sided confidence interval for the standard deviation.
22. In a typical car, bell housings are bolted to crankcase castings by means of a series
of 13 mm bolts. A random sample of 12 bolt-hole diameters is checked as part of
a quality control process and found to have a variance of 0.0013 mm2 .
a. Construct the 95% confidence interval for the variance of the holes.
b. Find the 95% confidence interval for the standard deviation of the holes.
23. Harris Interactive conducted a poll of American adults in August of 2011 to study
the use of online medical information. Of the 1,019 randomly chosen adults, 60%
had used the Internet within the past month to obtain medical information. Use the
results of this survey to create an approximate 95% confidence interval estimate for
the percentage of all American adults who have used the Internet to obtain medical
information in the past month.
24. The following is an excerpt from an August 2011
Just the Facts publication from
the Public Policy
Institute for California, “Because neither of the major political
parties has a majority of California’s registered voters, independents are influential
in statewide elections. For example, in the previous gubernatorial election, 54% of
the independents in our post-election survey said they voted for
Republican Arnold
Schwarzenegger. But in the 2008 presidential election, most independents (59%)
said they supported Democrat Barack Obama. In each case, the outcome reflected
the choice of the majority of independents.”
25. Suppose that the survey included 1011 independents. Find and interpret 99%
confidence interval for the proportion of California
independents who supported
Barack Obama in the 2008 presidential election.
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