exam 3 (missed) practice problems

A random sample of 80 observations results in 50 successes. What is the point estimate of the population proportion of successes?

0.625 (50/80=0.625)

A 95% confidence interval for the population mean is constructed as 6+/-2. What is the margin of error?

2

A 95% confidence interval for the population mean is calculated as (40,80). The margin of error for this interval is

20 [(40+80)/2=60 then 80-60=20]

What is the confidence level if a=0.10?

90%

An auditor for a small company suspects that the mean customer account balances have fallen below %550 per month, the average amount for all customer accounts over the past 5 years. She takes a random sample of 40 accounts and computes the sample mean as %543. State the hypotheses for testing the auditor's claim.

H0:u greater than or equal to 550 and Ha:u<550

A quality control officer believes that the average time of use for AAA batteries differs from the claimed 8.5 hours. The QC officer takes a random sample of the 30 AAA batteries and finds that the sample mean is 8.7 hours. State the null and alternative hypothesis for testing the officer's claim.

H0:u=8.5 and Ha:u not equal to 8.5

For a given sample size n, a can only be reduced

at the expense of increasing beta

A left-tailed test of the population mean is conducted at a=0.10. The calculated test statistic is z=-1.55 and P(Z<-1.55)=0.0606. The null hypothesis should _______.

be rejected since the p-values = 0.0606<0.10

All of the following are characteristics of the z and tdf distribution except

bimodal

Which one of the following is NOT the step we use when formulating the null and alternative hypotheses?

calculate the value of the sample statistic (we do not need this information when formulating the null and alternative hypotheses)

When examining the possible outcome of an election, what type of confidence interval is most suitable for estimating the current support for a candidate?

confidence interval for the population proportion

Whenever we construct a confidence interval for the population mean, the margin of error includes the standard error of x bar and the

desired level of confidence

A 95% confidence interval for the population mean implies that

for repeated samples, 95% of the sample means will fall within the interval

We can generally reduce Type I and Type II errors by

increasing the sample size

If we reject the null hypothesis when it is actually false we have committed

no error

In order to derive a confidence interval for u, the estimator x bar must have a

normal sampling distribution

A two-tailed test of the population mean is conducted at a=0.10. The calculated test statistic is z=-1.55 and P(Z<-1.55)=0.0606. The null hypothesis should _______.

not be rejected since the p-values =0.1212>0.10

The sampling distribution of the sample proportion can be approximated by a normal distribution when

np greater than or equal to 5 and n(1-p) is greater than or equal to 5

All of the following are components of the formula for selecting n to estimate u except

p^

When estimating the population mean, the tdf distribution is used when the

population variance is unknown

In a hypothesis test, u0 and p0 are hypothesized values of the _____ mean and the _____ proportion, respectively

population, population

Which of the following is a descriptive measure for a qualitative variable?

proportion

The mean and standard deviation are often used to describe ______ data while the proportion is a descriptive measure that can also be used for ____ data?

quantitative, qualitative

A confidence interval can be interpreted as a

range of values used to estimate an unknown population parameter

When testing u and sigma is known H0 can never be rejected if z less than or equal to 0 for a

right-tailed test

Hypothesis testing enables us to determine if the collected _____ data is inconsistent with what is stated in the null hypothesis

sample

Suppose you are constructing a confidence interval for the population mean. For a given confidence level and standard deviation, the width of the interval is wider for a

smaller sample size

When constructing a confidence interval for the population mean, the factors that affect the width of the confidence interval for a given standard deviation are

the confidence level and the sample size

The basic principle of hypothesis testing is to assume that

the null hypothesis is true and see if the sample data contradicts this assumption

true/false: the optimal values of Type I and type II errors require a compromise in balancing the costs of each type of error.

true