Statistic

Anonymous
timer Asked: Apr 3rd, 2017

Question Description

I have 25 Questiin need to be done in 2 hour exactly you can check the attachment file fir the questions.

1- Why would an analyst decide to select a simple random sample from a population? A. There are items in the population which might spoil the report, so it is best not to study those items. B. The analyst is wrong: it is always better to study the whole population. C. It is always better to study a sample than to study a population, therefore the sample must be selected. D. It might be that it is impossible to study each item in the population. 2- Select the true statement. A confidence interval may contain the population parameter, but it can happen that the population parameter is not in the interval. The bigger the sample size, the wider the confidence interval is. The wider the confidence interval, the more precise the estimation is. A confidence interval must contain the population parameter. 3- Find the false statement This is the example of a left-tailed test. This is the example of a valid hypothesis test . This is the example of a two-tailed test. This is the example of a right-tailed test. 4- z is drawn from the standard normal distribution and t is drawn from the Student's t-distribution with 7 degrees of freedom. Using Excel, match the pairs. Reft-tailed A. z-number is -1.35 probability is 0.089 B. t-number is -2.046 C. z-number is 0.253 Right-tailed D. t-number is 0.549 probability is 0.6 Right-tailed probability is 0.04 Left-tailed probability is 0.3 5- Select the true statements, using Excel. There may be more than one true statement. If you select a wrong statement, the mark will be reduced for this question. So, please do not guess. If standard deviation of the population is known to be 21 and the sample size is 68, the margin of error is 4.38, rounded to two decimal places. The level of confidence is 91%. If standard deviation of the sample is known to be 29 and the sample size is 6, the margin of error is 39.84, rounded to two decimal places. The level of confidence is 98%. If standard deviation of the sample is known to be 17 and the sample size is 15, the margin of error is 7.95, rounded to two decimal places. The level of confidence is 93%. If standard deviation of the population is known to be 15 and the sample size is 57, the margin of error is 4.08, rounded to two decimal places. The level of confidence is 96%. 6- A manager, who works for your company, said at a business meeting: We have asked employees who would volunteer to participate in the survey. We paid $100 to each employee for the participation, to be fair and compensate for the time spent answering the survey questions. Because of this, the participation was high and we could achieve the sample size of 130. Based on this sample, we found that the confidence interval for the proportion of happy employees in our company is [97.6%, 99.2%], with the confidence level of 95%. Please note that we had to use the Student's t-distribution with 95 degrees of freedom to find this confidence interval. Thus, our analysis has shown that at least 97.6% of our company's employees are very happy. What is wrong with the manager's statement? Keep in mind that this question allows multiple correct answers and incorrect answers will result in the mark reduction. The manager used an incorrect probability distribution to find the confidence interval. The manager must have used 99% confidence level. Not mentioning other errors, the manager used the incorrect number of degrees of freedom. The sample which the manager used was biased and therefore it could not be used for the statistical analysis. The sample size must have been bigger, because one cannot compute the confidence intervals with sample sizes with fewer than 150 items. Even if the manager had computed the confidence interval correctly, the manager failed to draw the correct conclusion. The mentioned confidence interval does not mean that at least 97.6% of employees are happy. 7- Pair each situation with the correct answer. Population standard deviation A. The mean of the sampling distribution of the is equal to $5. Sample size sample mean is $100. is 25. B. The standard deviation of the sampling distribution of the sample mean is $1. Population standard deviation is equal C. The standard deviation of the sampling to $1. Sample size is 16. distribution of the sample mean is $0.25 Population mean is $40. Sample size is 60. D. The mean of the sampling distribution of the sample mean is $40. Population mean is $100. Sample size is 50. 8- If z is drawn from the standard normal distribution, find the matching statements, using Excel. (Hint: P(z<0.5) means the probability that z is smaller than 0.5)) P(z < 0.3) P(z > 1.5) A. 0.354 B. 0.067 C. 0.618 P(1.4 < z < 1.9) D. 0.052 P(-1.5 < z < 0.2) 9- Select true statements. There might be several true statements. Each correct answer gives a mark. In you select an answer incorrectly, a mark will be subtracted. Therefore, please do not guess. Note that this question cannot earn a negative mark - the lowest mark for this question is 0. A. The bigger the sample size, the bigger is the standard deviation of the sampling distribution of the sample mean. B. The sampling distribution of the sample mean tends to become a bell-shaped distribution as the sample size increases. C. The mean of all possible sample means of a given size is exactly equal to the population mean. D. The standard deviation of the sampling distribution of the sample mean is bigger than the standard deviation of the population. 10 - A probability distribution of all possible sample means is called the ------- distribution of the sample mean. 11- In 2015, 56% of employed adults reported that mathematical skills were very important to their job. The supervisor of the job placement office at a college thinks that this percentage has increased due to increased use of technology in the workplace. She takes a random sample of 480 employed adults and finds that 297 of them feel that mathematical skills are very important to their job. Is there sufficient evidence to conclude that the percentage of employed adults who feel mathematical skills are very important to their job has increased at 0.05 level of significance? Please type the solution and the answer. Use the formula editor to enter numeric values and formulas. This question will be marked manually by your professor. 12A market research study in one Canadian city showed that the mean fare charged by taxi drivers is $21 and the standard deviation is $3.5. A random sample of 15 fares has been selected. What is the probability that the mean fare is between $20 and $23? Please type the solution and the answer. Use the formula editor to enter numeric values and formulas. This question will be marked manually by your professor. 13- Based on the analysis of a random sample consisting of 45 months, 96% confidence interval for the average monthly profit is [$100,566; $111,457]. Explain in less than 100 words what this means. 14- The best way to find out the average salary in your company is to perform a technique, known as Advanced Calibrated Sampling (ACS). This technique works in the following way: you must select a random sample of those employees, who have indicated that their salary is above $50,000 and exclude those, who indicated their salary to be above $100,000. Then you find the average salary of the selected employees. Agree Disagree 15- Consider the following test If the test statistic appears to be -2.34 and the critical value appears to be -2.3, should you accept the alternative hypothesis? Yes No 16- For the standard normal distribution, compute places. . Use Excel and round the answer to two decimal 17 - Using Excel, find the right-tail probability corresponding to the following t value. Round the answer to 4 decimal places. t = 1.456. There are 7 degrees of freedom. 18- Consider the following test performed with the level of significance 0.05: A random sample of size 39 is obtained from a normally distributed population. The population standard deviation is equal to 32.6. The sample mean happened to be 104.8. For this hypothesis test, what will be the critical value (the relevant z-alpha)? Hint: Watch the sign - the critical value can be negative or positive. Round the answer to three decimal places. 19- What is the proportion of customers who buy service plans when they buy a computer? To find out, you surveyed 134 customers and found that 46 purchased the service plan. What is the upper boundary of 90% confidence interval for the population proportion? Use Excel and round your answer to two decimal places. Give the answer as a decimal percent (that is, for 10%, give 0.1). 20- A poll is to be conducted to find out how many books, on average, Canadians read. You are the person who is to select a random sample and to ask the people of the sample about the number of books they read in the previous year. How many people are needed for your sample to estimate the number of books within 2 books with 90% confidence? Assume that it is known that the standard deviation for number of books read by Canadians is 12.3 books. 21- As a store manger you would like to find out the average time it takes to unload the truck which delivers the merchandise for your store. For this purpose, you have taken a random sample of 35 days and found the average unload time to be 294 minutes for the sample. You also found that the standard deviation is 27 minutes for the sample. Find the upper boundary of the 95% confidence interval for the average unload time. Round the answer to two decimal places. 22- For the Student's t-distribution with 15 degrees of freedom, compute answer to two decimal places. . Use Excel and round the 23- It is known that the average return on a stock is 29.5% with the standard deviation equal to 21.8%. A simple random sample of 90 returns is to be selected and the average return of the sample is to be found. You can say that this sample average is a random variable. What is the standard deviation of this random variable? Round your answer to 2 decimal places. 24- Consider the following test: A random sample of size 23 is obtained from a population that is known to be normally distributed with the population standard deviation equal to 12.2. If the sample mean happened to be 52.1, compute the test statistic. Round the answer to two decimal places. 25- The null hypothesis is assumed to be true until evidence indicates otherwise. True False

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