Estimation of Population

A sample size of n = 64 is drawn from a population whose standard deviation is σ = 5.6.

Find the margin of error for a 99% confidence interval for µ.

• 1.799

• 1.798

• 1.803

An IQ test was given to a simple random sample of 75 students at a certain college. The sample mean score was 105.2. Scores on this test are known to have a standard deviation of 10. It is desired to construct a 90% confidence interval for the mean IQ scores of the students at the college. Find the Margin of Error to two decimal places.

• 1.90

• 1.89

• 1.899

• 1.99

The lifetime of a certain type of batter is known to be normally distributed with a standard deviation of 20 hours. A sample of 50 batteries had a mean lifetime of 120.1 hours. It is desired to construct a 99% confidence interval for the mean lifetime of this type of battery. What is the Confidence Interval to one decimal place?

• (114.5, 125.6)

• (112.8, 127.4)

• (112.82, 127.38)

• (114.56, 125.64)

If the 95% Confidence Interval for a population mean is (114.56, 125.54), then is it likely that the true population mean µ is greater than 130?

• Yes

• No

• Not enough information

• I have no idea what you're asking of me

A quality control specialist at a glass factory must estimate the mean clarity rating for a new batch of glass using a sample of 18 glass sheets from the batch. Past investigations show that clarity ratings are normally distributed. The specialist decides to use a t-distribution rather than a z-distribution because ...

• The t distribution is more accurate than a z distribution.

• Clarity ratings for the entire bacth are normally distributed.

• The t-distribution will create a narrower interval than z.

• The standard deviation for the population is unknown.

In a crash test of 15 troopers, collision repair costs are found to have a distribution that is approximately normal, with a mean of $1800 and a standard deviation of $950. Construct a 99% confidence interval for the repair cost for the population.

• (1070, 2530)

• (1273, 2326)

• (1799, 1801)

• (1776, 1823)

STATEMENT 1: Joy collected information from 15 students and wants to determine the confidence interval estimate of their monthly allowance using a confidence level of 95%? It is appropriate to use a critical value of 2.145 for that test/experiment, given that the sample standard deviation is known.

STATEMENT 2: Estimator is the process of making generalization and inferences about the population parameter using sample statistics.

• Both Statements are True

• Both Statements are False

• Statement 1 is True and Statement 2 is False

• Statement 1 is False and Statement 2 is True

The confidence level and narrowness of the interval are some things to consider to determine a sample size.

In determining sample sizes, it is important that the margin of error is known.

• Both Statements are True

• Both Statements are False

• Statement 1 is True and Statement 2 is False

• Statement 1 is False and Statement 2 is True

When the confidence level is 95%, n>30 and the population parameters are known, the critical value to be used to compute for the sample size is 1.96.

Since the variation in the population is used to determine a confidence interval, then it will no longer be used to determine sample sizes.

• Both Statements are True

• Both Statements are False

• Statement 1 is True and Statement 2 is False

• Statement 1 is False and Statement 2 is True

Suppose a 95% confidence interval for \mu_1-\mu_2 is (-2.13,1.48), what can you conclude?

• We are 95% confident that there is no difference between the population means.

• We are 95% confident that there is a difference between the population means.