Explore BrainMass

Confidence Interval

Conference interval

A consulting firm which does consulting jobs on a cost per job basis wants to estimate its average pay per hour. The firm's manager takes a random sample of n=30 jobs and calculates the pay per an hour. The par per an hour values are listed below, rounded to the nearest dollar. 17 23 14 20 68 40 31 19 19 32 13 37 32 28 34 23 2

Confidence Interval for true mean

A savings and loan association needs information concerning the checking account balances of it's local customers. A random sample of 14 accounts was checked, yielding the following balances (rounded to the nearest dollar): 701 379 349 828 499 174 786 762 580 943 741 798 311 1096 Find a 99% confidence interval for the true me

Compute a 95% confidence interval for the standard deviation of the above data.

A financial analyst, known for her excellent track record, has decided to part company with her old partners and to enter the venture capital area. In it's publicity brochure, the firm she joins lists the market adjusted rate of return that their new partner achieved during her previous tenure. The table below shows these return


In an election campaign, the party vying for an upset polls a sample of 100 voters. The party finds that 60 of 100 clearly express the intention of voting in favor of the party polling. How many voters should be sampled if the party wants to estimate the population proportion with a sampling error of 5% or less? (Use confide

Confidence interval for the difference of proportions

Please help with the following problem. Provide step by step calculations. After a certain candidate announced his intention for running for the premiership of a province, many polls were conducted to assess his chanced for success. Among them were two polls of independant samples taken from two populations. The poll in the

Confidence intervals and prediction intervals

Day 1 dose 123 Day 2 dose 139 Day 3 dose 85 Day 4 dose 133 Day 5 dose 91 Day 6 dose 110 Day 7 dose 118 What is the 95% one-sided confidence interval for the average worker? What is the 95% predicted dose for a 95% one-sided confidence interval?

A sample problem is solved.

Given the following information, calculate a confidence interval using a 95 percent confidence level: sample proportion =.4, standard error of the proportion =.05, and sample size =100.

Confidence intervals and hypothesis testing? Maybe?

A local merchant is interested in obtaining a small business loan to expand his business. He will be able to obtain a more favorable interest rate if he can reasonably demonstrate that his near-term monthly revenues will be between $10,000 and $15,000. He doesn't know the exact level of sales to expect over the next several mo

Confidence Intervals

A cutoff score of 79 has been established for a sample of scores in which the mean is 65. If the corresponding z-score is 1.4 and the scores are normally distributed, what is the standard deviation?

Confidence Interval

How do you figure a 90% confidence interval for the mean weight of all Siberian tigers in captivity from various zoo's, where the random sample is 31, the mean weight is 507 pounds from sample zoo's, with a standard deviation of 62 pounds?

Confidence Interval

Which of the following is not needed to be known to calculate a confidence interval? a. standard deviation b. sample size c. mean d. degree of confidence

Confidence Interval and Statistical Analysis

Find the confidence interval and conduct statistical analysis for the given problems. 6. A producer of a juice drink advertises that it contains 10% real fruit juices. A sample of 75 bottles of the drink is analyzed and the percent of real fruit juices is found to be 6.5%. If the true proportion is actually .10, what is th

Probability/Confidence Level

1) Megacorp wants to determine whether the mean of all one-day travel expenses in Moscow exceeds $500. A simple random sample of 35 one-day travel expenses is obtained from Megacorp travel expense files. The average one-day Moscow expense was found to be $538 with a standard deviation of $41. a) Calculate the probability of

Statistic problem

2 Questions: 3) Using the CIELO data, calculate 95% and 99% confidence intervals for the percentage intending to purchase the CIELO. (see attachment for full question) -------------------------------------------------- 3) Using the CIELO data, calculate 95% and 99% confidence intervals for the Percentage intending to purcha

Calculate 95% and 99% confidence intervals for the mean selling price of vehicles sold by Winter Pontiac. Test the hypothesis that the mean selling price of automobiles sold by Winter Pontiac is less than $25,000. Use alpha= .05

1)      Calculate 95% and 99% confidence intervals for the means selling price of Vehicles sold by Winter Pontiac. 2)      Test the hypothesis that the mean selling price of automobiles sold by Winter Pontiac is less than $25,000. Use alpha= .05 To solve the problem 1 and 2 below use the following table

Statistics - Confidence Interval

Please provide step by step instructions using actual numbers instead of formulas for solving the following 3 problems, thanks 3. Determine whether the average number of calories in a homemade cookie is more than a store-bought one. Estimate the difference in the mean calories between the two types using a 90% confidence int

Confidence interval level

I have an opinion poll perfomed on 2 different population sizes, 900 and 10,000 with a 95% confidence level (Confidence Interval details have been computed) for each population. Opinion Poll Surveyed 900 Surveyed 10000 Invalid intelligence 52% 468 Invalid Intelligence 52% Proportion 0.52 Proportion 0.52

Test a Hypothesis and Confidence Interval

Case Analysis: Riverside Chamber of Commerce ABC Corporation of California publishes a variety of statistics, including the number of individuals who got a new job during the past 12 months and the mean length of time the individuals have been on the job. The Statistical Analysis Department of ASBC Corporation reported that th


4.) 20 rivets out 100 in a new box that we tested had break strength below the desired level. Since this is a critical part for assembly, we want to be 99% confident of how many rivets are below the desired level. Calculate the confidence interval of the percentage of rivets that are below the desired level. 5.) We expect a 1

Statistics: Confidence Interval and Decision Making

Tourism is one consideration for CoffeeTime's future. A survey of 1,233 visitors to Mumbai last year revealed that 110 visited a small café. Use a 0.05 significance level to test her claim. Would it be wise for her to use that claim in trying to convince management to increase their advertising spending to travel agents? Ex

Comparisons Involving Proportions and a Test of Independence

Does age make a difference in the amount of savings a worker feels is needed to be secure at retirement? A study by CommSciences for Transamerica Asset Management found that 0.24 of workers in the 25-33 age category feel that $250,000 to $500,000 is enough to be secure at retirement. In the 34-52 age category already 0.35

Confidence intervals for one population mean

For a t-curve with df = 8, find each t-value and illustrate your results graphically. a.The t-value having area 0.05 to its right. b. t 0.10 c.The t-value having area 0.01 to its left (hint: A t-curve is symmetric about 0.) d.The two t-values that divide the area under the curve into a middle 0.95 area and two outsid

Test whether the sample has been drawn from the population.

A Variable has a mean of 100 and a standard deviation of 16. Four observations of this variable have a mean of 108 and a sample standard deviation of 12. Test whether the sample has been drawn from the population. a. Standardized version of x (sample mean). b. Studentized version of x (sample mean).


5. Human body temperatures are normally distributed with a mean of 98.6 degrees F and a standard deviation of 0.72 deg. F. Find the temperature that separates the top 7% from the bottom 93%. 6. In a sample of 49 adolescents who served as the subjects in an immunologic study, one variable of interest was the diameter of skin

Confidence Interval

1) a statistian claims that the average score on a test of students for students who major in psychology is greater than that of students who major in math results given to 50 students in each group are shown here Is there enough evidence to support the statisticians claim at @=0.01 Show work. Physc Math X1=118

Confidence Interval

Using sample results and level of confidence of 0.01, test to determine whether the figure published by Runzheimer International is too high. Was it a one- or two-tailed test?

Conditional probability

4) In a survey conducted to determine cost of vacations, 164 individuals were randomly sampled. Each person was asked to assess the total cost of his or her most recent vacation. The average cost was $1,386. Assuming that the standard deviation was $400, find a 94% confidence interval for the average cost of all vacation trips.

Working with confidence levels.

I randomly selected 200 likely voters and created a 95 percent confidence interval for the true proportion of voters that will vote for my candidate. My confidence interval has endpoints of 0.39 and 0.45. Given the confidence interval that I created, is my candidate going to win? After constructing the confidence interval I call