# 9.8 Exercises  (Page 5/5)

 Page 5 / 5

A camp director is interested in the mean number of letters each child sends during his/her camp session. The population standard deviation is known to be 2.5. A survey of 20 campers is taken. The mean from the sample is 7.9 with a sample standard deviation of 2.8.

• $\overline{x}=\text{________}$
• $\sigma =\text{________}$
• ${s}_{x}=\text{________}$
• $n=\text{________}$
• $n-1=\text{________}$
• Define the Random Variables $X$ and $\overline{X}$ , in words.
• Which distribution should you use for this problem? Explain your choice.
• Construct a 90% confidence interval for the population mean number of letters campers send home.
• State the confidence interval.
• Sketch the graph.
• Calculate the error bound.
• What will happen to the error bound and confidence interval if 500 campers are surveyed? Why?

• 7.9
• 2.5
• 2.8
• 20
• 19
• $N\left(7\text{.}9,\frac{2\text{.}5}{\sqrt{\text{20}}}\right)$
• CI: (6.98, 8.82)
• EB: 0.92

Stanford University conducted a study of whether running is healthy for men and women over age 50. During the first eight years of the study, 1.5% of the 451 members of the 50-Plus Fitness Association died. We are interested in the proportion of people over 50 who ran and died in the same eight–year period.

• Define the Random Variables $X$ and $P\text{'}$ , in words.
• Which distribution should you use for this problem? Explain your choice.
• Construct a 97% confidence interval for the population proportion of people over 50 who ran and died in the same eight–year period.
• State the confidence interval.
• Sketch the graph.
• Calculate the error bound.
• Explain what a “97% confidence interval” means for this study.

In a recent sample of 84 used cars sales costs, the sample mean was $6425 with a standard deviation of$3156. Assume the underlying distribution is approximately normal.

• Which distribution should you use for this problem? Explain your choice.
• Define the Random Variable $\overline{X}$ , in words.
• Construct a 95% confidence interval for the population mean cost of a used car.
• State the confidence interval.
• Sketch the graph.
• Calculate the error bound.
• Explain what a “95% confidence interval” means for this study.

• ${t}_{\text{83}}$
• mean cost of 84 used cars
• CI: (5740.10, 7109.90)
• EB = 684.90

A telephone poll of 1000 adult Americans was reported in an issue of Time Magazine . One of the questions asked was “What is the main problem facing the country?” 20% answered “crime”. We are interested in the population proportion of adult Americans who feel that crime is the main problem.

• Define the Random Variables $X$ and $P\text{'}$ , in words.
• Which distribution should you use for this problem? Explain your choice.
• Construct a 95% confidence interval for the population proportion of adult Americans who feel that crime is the main problem.
• State the confidence interval.
• Sketch the graph.
• Calculate the error bound.
• Suppose we want to lower the sampling error. What is one way to accomplish that?
• The sampling error given by Yankelovich Partners, Inc. (which conducted the poll) is ± 3%. In 1-3 complete sentences, explain what the ± 3% represents.

Refer to the above problem. Another question in the poll was “[How much are] you worried about the quality of education in our schools?” 63% responded “a lot”. We are interested in the population proportion of adult Americans who are worried a lot about the quality of education in our schools.

1. Define the Random Variables $X$ and $P\text{'}$ , in words.
2. Which distribution should you use for this problem? Explain your choice.
3. Construct a 95% confidence interval for the population proportion of adult Americans worried a lot about the quality of education in our schools.
• State the confidence interval.
• Sketch the graph.
• Calculate the error bound.
4. The sampling error given by Yankelovich Partners, Inc. (which conducted the poll) is ± 3%. In 1-3 complete sentences, explain what the ± 3% represents.

• $N\left(0.63,\sqrt{\frac{\left(0.63\right)\left(0.37\right)}{1000}}\right)$
• CI: (0.60, 0.66)
• EB = 0.03

Six different national brands of chocolate chip cookies were randomly selected at the supermarket. The grams of fat per serving are as follows: 8; 8; 10; 7; 9; 9. Assume the underlying distribution is approximately normal.

• Calculate a 90% confidence interval for the population mean grams of fat per serving of chocolate chip cookies sold in supermarkets.
• State the confidence interval.
• Sketch the graph.
• Calculate the error bound.
• If you wanted a smaller error bound while keeping the same level of confidence, what should have been changed in the study before it was done?
• Go to the store and record the grams of fat per serving of six brands of chocolate chip cookies.
• Calculate the mean.
• Is the mean within the interval you calculated in part (a)? Did you expect it to be? Why or why not?

A confidence interval for a proportion is given to be (– 0.22, 0.34). Why doesn’t the lower limit of the confidence interval make practical sense? How should it be changed? Why?

## Try these multiple choice questions.

The next three problems refer to the following: According to a Field Poll, 79% of California adults (actual results are 400 out of 506 surveyed) feel that “education and our schools” is one of the top issues facing California. We wish to construct a 90% confidence interval for the true proportion of California adults who feel that education and the schools is one of the top issues facing California. (Source: http://field.com/fieldpollonline/subscribers/)

A point estimate for the true population proportion is:

• 0.90
• 1.27
• 0.79
• 400

C

A 90% confidence interval for the population proportion is:

• (0.761, 0.820)
• (0.125, 0.188)
• (0.755, 0.826)
• (0.130, 0.183)

A

The error bound is approximately

• 1.581
• 0.791
• 0.059
• 0.030

D

The next two problems refer to the following:

A quality control specialist for a restaurant chain takes a random sample of size 12 to check the amount of soda served in the 16 oz. serving size. The sample mean is 13.30 with a sample standard deviation of 1.55. Assume the underlying population is normally distributed.

Find the 95% Confidence Interval for the true population mean for the amount of soda served.

• (12.42, 14.18)
• (12.32, 14.29)
• (12.50, 14.10)
• Impossible to determine

B

What is the error bound?

• 0.87
• 1.98
• 0.99
• 1.74

C

What is meant by the term “90% confident” when constructing a confidence interval for a mean?

• If we took repeated samples, approximately 90% of the samples would produce the same confidence interval.
• If we took repeated samples, approximately 90% of the confidence intervals calculated from those samples would contain the sample mean.
• If we took repeated samples, approximately 90% of the confidence intervals calculated from those samples would contain the true value of the population mean.
• If we took repeated samples, the sample mean would equal the population mean in approximately 90% of the samples.

C

The next two problems refer to the following:

Five hundred and eleven (511) homes in a certain southern California community are randomly surveyed to determine if they meet minimal earthquake preparedness recommendations. One hundred seventy-three (173) of the homes surveyed met the minimum recommendations for earthquake preparedness and 338 did not.

Find the Confidence Interval at the 90% Confidence Level for the true population proportion of southern California community homes meeting at least the minimum recommendations for earthquake preparedness.

• (0.2975, 0.3796)
• (0.6270, 6959)
• (0.3041, 0.3730)
• (0.6204, 0.7025)

C

The point estimate for the population proportion of homes that do not meet the minimum recommendations for earthquake preparedness is:

• 0.6614
• 0.3386
• 173
• 338

A

can someone help me with some logarithmic and exponential equations.
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
a perfect square v²+2v+_
kkk nice
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
rolling four fair dice and getting an even number an all four dice
Kristine 2*2*2=8
Differences Between Laspeyres and Paasche Indices
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
is it 3×y ?
J, combine like terms 7x-4y
im not good at math so would this help me
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!