Questions on Confidence Intervals. Construct interval, find sample size, interpret the confidence level answered by real tutors!

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Question 934901: To determine the mileage of a new model automobile, a random sample of 36 cars was tested. A
sample with a mean of 32.6 mpg and a standard deviation of 1.6 mpg was obtained. Construct the 90%
confidence interval for the actual mean mpg of the population of this model automobile.
Click here to see answer by stanbon(75887)

Question 934899: A random sample of 41 NBA players gave a standard deviation s = 3.32 inches for their height. How many more NBA players have to be included in the sample to make 95% sure that the sample mean �x of their height is within 0.75 inch of the mean � of the height of the population of all NBA players.
Click here to see answer by stanbon(75887)

Question 934898: A wildlife study is designed to find the mean weight of salmon caught by an Alaskan fishing company. As a preliminary study, a random sample of 50 freshly caught salmon is weighed. The sample standard deviation is 2.15 pounds. How large a sample should be taken to be 99% confident that the sample mean is within 0.20 pound of the true mean weight?

Click here to see answer by stanbon(75887)

Question 935140: A chocolate factory produces mints that weigh 10 grams apiece. The standard deviation of the weight of a box of 10 mints is 3 grams. You buy a box that weighs 95 grams. What is your confidence that the box you bought did not come from the factory.
I am not familiar with confidence intervals, and there isn't a sample size given in this word problem. Can anyone help me out?
Click here to see answer by Theo(13342)

Question 953260: when 274 college students are randomly selected and surveyed, it is found that 123 own a car. find a 99% confidence interval for the true proportion of all college students who own a car.

Click here to see answer by stanbon(75887)

Question 958256: a random sample of 31 juice drinks has a mean of 99.3 and a standard deviation 41.5 calories. Construct a 95% confidence interval for the population mean number of calories per juice drink.
My problem is that i dont know how to plug the numbers into the equation, and which numbers should i worry about.
Click here to see answer by stanbon(75887)

Question 970873: which of the following relations is not a function ?
a. {(5, 11), (6, 2), (3, 2), (4, 7), (1, 3)}
b. {(1, 11), (6, 2), (3, 4), (5, 7), (8, 12)}
c. {(1, 11), (6, 2), (3, 4), (9, 7), (8, 12)}
d. {(1, 5), (6, 2), (3, 4), (5, 7), (6, 12)}

Click here to see answer by MathLover1(20850)

Question 970870: a company that manufactures a certain item has a fixed cost of $12,000. additionally it costs $15 to produce each item , items are sold at $30 per pair. what is the break-even point.
a. (1,400, $42,000)
b. 1,200, $36,000)
c. (1,000,$30,000)
d. (800, $24,000)
Click here to see answer by rfer(16322)

Question 970866: which of the following system of linear equations has an infinite number of solutions?
a. x+3y=10, 4x+12y=40
b. x+y=11, x-y=2
c. x+y=11, 2x-y=6
d. 2x+y=8, 4x+2y=11
Click here to see answer by reviewermath(1029)

Question 970857: which of the following intervals represents the set (1,4)∩[2, 6]
a. [2, 4
b. 4, ]
c. [1, 6)
d. (1, 2]
Click here to see answer by josgarithmetic(39630)

Question 997813: What does, "during the interval of 30 to 40 minutes" mean?
Does it mean 10 minutes?
(I know it's silly, but I'm just over thinking it.)
Click here to see answer by fractalier(6550)

Question 1002631: 1/((1/x)+1) how t becomes x/x+1
Click here to see answer by Alan3354(69443)

Question 1006453: solve on the interval (0, 2pi)
cos(4X) - cos(6X) = 0

Click here to see answer by harrysu321@gmail.com(1)

Question 1006453: solve on the interval (0, 2pi)
cos(4X) - cos(6X) = 0

Click here to see answer by ikleyn(52886)

Question 1011928: Please help me solve this question
If 'a' is the length of one of the sides of an equilateral triangle ABC, base BC lies on X - axis and vertices B is at the origin, find the coordinates of the vertices of triangle ABC
Click here to see answer by josgarithmetic(39630)

Question 1013012: A sample of 29 federally sentenced adult male prisoners had an average sentence of 9 years. Assume that, for federally sentenced adult male prisoners in this sample, the sample standard deviation of sentence length is 17 years. Compute a 90% confidence interval for the mean sentence length, , of all federally sentenced adult male prisoners.
Click here to see answer by stanbon(75887)

Question 1019784: Find an equation for the secant line through the points where x has the given values
y=6√x
x=1
x=4
Click here to see answer by ikleyn(52886)

Question 1019791: Need help with this Calculus problem please.

Find an equation for the secant line through the points where x has the given values.
y=3√x
x=4
x=9
Click here to see answer by ikleyn(52886)

Question 1023218: Can some please help me with these questions! I'm lost!
Use the properties of determinants to find the following determinants without a full set of calculations!
1) |243 0 -387|
Find |26 0 -98|
|598 0 4891|
2)
|3 0 -3|
IF |2. 1. 0|
|0 -2 -1|
,then find |6 0 -3|
|4 1 0|
|0 -2 -1|
3)
If |3 0 -3|
|2 1 0|=9
|0-2 -1|
,then find
| 3. 0. -3|
|(2+0) (1-2) (0-1)|
| 0. -2 -1|
Click here to see answer by robertb(5830)

Question 1024223: Find the derivative using the product rule?
y=(x+1)(9√x +8
Click here to see answer by solver91311(24713)

Question 1029100: Calculus:
A fence must be built to enclose a rectangular area of 5000 ft^2. Fencing material costs $1 per foot for the two sides facing north and south and $2 per foot for the other two sides.
Find the cost of the least expensive fence.
Click here to see answer by stanbon(75887)

Question 1031920: What is six less then the quoting of a number and two is thirteen?

Click here to see answer by stanbon(75887)

Question 1031954: How much sugar is in a cookie with reduced sugar?
A random sample of 20 reduced-sugar cookies were tested in a lab, the mean sugar content was 3.2 grams and the standard deviation was 1.1 grams of sugar.

a) Construct a 95% confidence interval for the mean grams of sugar. (Round your answers to two decimal places).
b) Interpret the results of part a.

Click here to see answer by stanbon(75887)

Question 1039810: How do you find the margin of error?
(24, 25, 26, 27, 28, 29, 30, 31, 32) but it doesn't give a percent number?
Click here to see answer by stanbon(75887)

Question 1039809: How do you find the width of a confidence interval?

Click here to see answer by stanbon(75887)

Question 1039813: Determine the min. sample size needed to be 94% confident that the sample mean we get is within 1/4 inch of the true mean.
n=33, mean=69.606, s= 3.010
Click here to see answer by stanbon(75887)

Question 1039842: How do you find the degrees of freedom for 93% when you subtract 33-1=32 and find 32 on the tdistribution under 93%?
Click here to see answer by Edwin McCravy(20064)

Question 1040001: When it asks which confidence interval is wider or which sample size requirement is larger, what do you say when it asks you why?
Click here to see answer by Boreal(15235)

Question 1040099: Determine the minimum sample size needed to be 94% confident that the sample mean we get is within 1/2 inch of the true mean.
n=33, mean=69.606, s= 3.010
Click here to see answer by stanbon(75887)

Question 1040098: I'm having trouble with questions like this. I know you are suppose to use t when sigma is unknown.
Construct a 93% confidence interval for the mean height of the entire student body. (round to 3 decimal places) (size =33, mean=69.606, standard deviation=3.010)
How do I set it up to get the correct answer?
Click here to see answer by stanbon(75887)

Question 1041478: A teacher is comparing test grades for a yearly test in her Algebra class. The
mean of the scores is 78% and has a standard deviation of 3.8. Which range gives the set of values that are within two standard deviations of the mean?
A.) 74.2 - 81.8
B.) 70.4 - 85.6
C.) 74.2 - 85.6
D.) 70.4 - 81.8

Click here to see answer by jim_thompson5910(35256)

Question 1055491: why is a 99% confidence interval wider than 95% confidence interval?
Click here to see answer by ewatrrr(24785)

Question 1055505: What is meant by the term �90% confident� when constructing a confidence interval for a mean?
a. If we took repeated samples, approximately 90% of the samples would produce the same confidence interval.
b. If we took repeated samples, approximately 90% of the confidence intervals calculated from those samples would
contain the sample mean.
c. If we took repeated samples, approximately 90% of the confidence intervals calculated from those samples would
contain the true value of the population mean.
d. If we took repeated samples, the sample mean would equal the population mean in approximately 90% of the
samples.
Click here to see answer by ewatrrr(24785)

Question 1058988: Suppose you construct 1000 confidence intervals of the mean US household annual income. If you use a 94% level of confidence, about how many of these intervals will actually contain the true mean US household annual income?
Click here to see answer by math_helper(2461)

Question 1060701: how do I find a 95% confidence interval for the true proportion of all medical students who plan to work in a rural community. given the population proportiob p of 380 randomlty selected medical students, 21 said that they planned to work in a rural community.
Click here to see answer by rothauserc(4718)

Question 1060766: Suppise you are told that a 95% confidence interval for the average price of gasoline in your state is from $3.37 to $3.89. Use the fact that the confidence interval for the mean is in the former x -E to x + E to compute the sample mean and the maximal margin of error E
Click here to see answer by MathTherapy(10557)

Question 1061629: 11. Suppose a 95% confidence interval is computed forμresulting in the interval (112.4, 121.6).
Then it would be accurate to say
A. 95% of the time,μfalls within the interval (112.4, 121.6).
B. There is a 95% chance thatμwill fall within the interval (112.4, 121.6).
C. 5% of all the possible samples will produce intervals that do captureμ.
D. 95% confident that the true value for μwill fall within the interval (112.4, 121.6).
Click here to see answer by Boreal(15235)

Question 1062600: A sample of 400 nursing applications included 220 from women. Find the 95% confidence interval of the true proportion of women who applied to the nursing program.
Click here to see answer by rothauserc(4718)

Question 1062601: In a survey of 1000 drivers in the entire province about using of cellphones while driving, 423 admitted that they are doing it while driving. a) Find p(p hut) b) find q(q hut)
Click here to see answer by Boreal(15235)

Question 1062599: A sample of 21 is taken from a normal distributed population. The sample has a mean of 40 and a standard deviation of 3.2. Construct a confidence interval if it is 95% level of confidence.
Click here to see answer by Fombitz(32388)

Question 1080028: Lifetimes of AAA batteries are approximately normally distributed. A manufacturer wants to estimate the standard deviation of the lifetime of the AAA batteries it produces. A random sample of
22
AAA batteries produced by this manufacturer lasted a mean of
10.1
hours with a standard deviation of
1.9
hours. Find a
90%
confidence interval for the population standard deviation of the lifetimes of AAA batteries produced by the manufacturer. Then complete the table below.
Carry your intermediate computations to at least three decimal places. Round your answers to at least two decimal places.
Click here to see answer by Boreal(15235)

Question 1084647: A supermarket manager wishes to make an estimate of the average time in minutes a customer spends at the checkout counter. It is known from previous studies that the variance is 10.8. How large a sample is required if she wants a 95% confidence interval for the population mean that extends no further than 0.7 minutes from the sample mean. Round up your answer to a whole number.
I gound the answer to be 8468 but it is incorrect.
Click here to see answer by jim_thompson5910(35256)

Question 1105509: The distribution of income (in minimum salaries) of the certain city population is given below:
(%): 54 | 23 | 10 | 5 | 8 |
Income range: (0-2] (2-4] (4-6] (6-10] (No statement]
Get a new income distribution, considering only the people who declare some income. From the distribution obtained by you, calculate:
a) The average income;
b) The proportion of people receiving up to 1.5 minimum wages.
c) The income range corresponding to the richest 10%.

Click here to see answer by Alan3354(69443)

Older solutions: 1..45, 46..90, 91..135