STAT 2510 EXAM 3 QUESTIONS AND
ANSWERS GRADED A+ 2026
Based on a sample of size 42, a 95% confidence interval for the mean score of all students μ, on
an aptitude test is from 57.1 to 64.9. Find the margin of error. - ANS 3.9
A 90% two-sided confidence interval for u which has been calculated using some software turns
out to be (2.2 and 3.5)
2. You can be 90% confident that μ is between 2.2 and 3.5.
3. A 95% two-sided confidence interval based on the same date will contain the value 0.9. -
ANS Yes
Cannot tell
Use the given 95% confidence interval for a parameter μ to decide whether each statement is
true or false.
Based on a two-sided confidence interval (33.2, 44.5) we conclude that the parameter μ is
significantly different from 30. - ANS True
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, A sample of 40 washing machines yields a mean replacement time of 11.5 years. Assuming that
σ = 2.4 years, find the margin of error in estimating μ at the 90% level of confidence. -
ANS 0.6 years
Weights of women in one age group are normally distributed with a standard deviation σ of 10
lb. A researcher wishes to estimate the mean weight of all women in this age group. Find how
large a sample must be drawn in order to be 90 percent confident that the sample mean will
not differ from the population mean by more than 3.4 lb. - ANS 24
Thirty random selected students took the calculus final. If the sample mean was 92 and the
standard deviation was 8.8 (x bar = 92 , s = 8.8), construct a 99% confidence interval for the
mean score of all students. - ANS 87.57 to 96.43
The recommended dietary allowance (RDA) of vitamin C for women in 75 milligrams per day. A
hypothesis test is to be performed to decide whether adult women are, on average, getting less
than RDA of 75 milligrams per day. - ANS H0: μ = 75 mg versus Ha: μ < 75 mg
In the past, the mean running time for a certain type of flashlight battery has been 9.2 hours.
The manufacturer has introduced a change in the production method and wants to perform a
hypothesis test to determine whether the mean running time has increased as a result.
The hypothesis are:
Ho: μ= 9.2 hours vs Ha: μ > 9.2 hours, where μ is the mean running time of the new batteries.
Suppose that the results of the sampling lead to NON-REJECTION of the null hypothesis (do not
reject Ho. Classify that conclusion as a Type I error, a Type II error, or a correct decision, if in fact
the mean running time has increased. - ANS Type II error
A sample mean, sample size, and population standard deviation are given. Use the one mean z-
test to perform the required hypothesis test at a given significance level.
x= 25, n= 40, σ = 1.5, Ho: μ = 22; Ha: μ = 22; α = 0.05 - ANS z0 = 12.65; critical value = ±1.96;
reject H0
Use the one-proportion z-interval procedure to find the required confidence interval. A study
involves 660 randomly selected deaths, with 30 of them caused by accidents. Construct a 98%
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
ANSWERS GRADED A+ 2026
Based on a sample of size 42, a 95% confidence interval for the mean score of all students μ, on
an aptitude test is from 57.1 to 64.9. Find the margin of error. - ANS 3.9
A 90% two-sided confidence interval for u which has been calculated using some software turns
out to be (2.2 and 3.5)
2. You can be 90% confident that μ is between 2.2 and 3.5.
3. A 95% two-sided confidence interval based on the same date will contain the value 0.9. -
ANS Yes
Cannot tell
Use the given 95% confidence interval for a parameter μ to decide whether each statement is
true or false.
Based on a two-sided confidence interval (33.2, 44.5) we conclude that the parameter μ is
significantly different from 30. - ANS True
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, A sample of 40 washing machines yields a mean replacement time of 11.5 years. Assuming that
σ = 2.4 years, find the margin of error in estimating μ at the 90% level of confidence. -
ANS 0.6 years
Weights of women in one age group are normally distributed with a standard deviation σ of 10
lb. A researcher wishes to estimate the mean weight of all women in this age group. Find how
large a sample must be drawn in order to be 90 percent confident that the sample mean will
not differ from the population mean by more than 3.4 lb. - ANS 24
Thirty random selected students took the calculus final. If the sample mean was 92 and the
standard deviation was 8.8 (x bar = 92 , s = 8.8), construct a 99% confidence interval for the
mean score of all students. - ANS 87.57 to 96.43
The recommended dietary allowance (RDA) of vitamin C for women in 75 milligrams per day. A
hypothesis test is to be performed to decide whether adult women are, on average, getting less
than RDA of 75 milligrams per day. - ANS H0: μ = 75 mg versus Ha: μ < 75 mg
In the past, the mean running time for a certain type of flashlight battery has been 9.2 hours.
The manufacturer has introduced a change in the production method and wants to perform a
hypothesis test to determine whether the mean running time has increased as a result.
The hypothesis are:
Ho: μ= 9.2 hours vs Ha: μ > 9.2 hours, where μ is the mean running time of the new batteries.
Suppose that the results of the sampling lead to NON-REJECTION of the null hypothesis (do not
reject Ho. Classify that conclusion as a Type I error, a Type II error, or a correct decision, if in fact
the mean running time has increased. - ANS Type II error
A sample mean, sample size, and population standard deviation are given. Use the one mean z-
test to perform the required hypothesis test at a given significance level.
x= 25, n= 40, σ = 1.5, Ho: μ = 22; Ha: μ = 22; α = 0.05 - ANS z0 = 12.65; critical value = ±1.96;
reject H0
Use the one-proportion z-interval procedure to find the required confidence interval. A study
involves 660 randomly selected deaths, with 30 of them caused by accidents. Construct a 98%
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
