2025 MATH 221 STATISTICS FINAL EXAMS QUESTIONS WITH
ANSWERS GRADED A+ 2025/2026
If a confidence interval is given from 8.52 to 10.23 and the mean is known to be 9.375,
what is the maximum error?
0.428
1.710
0.855
8.520 - 0.855
Which of the following is most likely to lead to a large margin of error?
small mean
large sample size
small sample size
small standard deviation - small sample size
From a random sample of 41 teens, it is found that on average they spend 31.8 hours
each week online with a population standard deviation of 3.65 hours. What is the 90%
confidence interval for the amount of time they spend online each week?
(30.86, 32.74)
(29.99, 33.61)
(24.50, 39.10)
(28.15, 35.45) - (30.86, 32.74)
A company making refrigerators strives for the internal temperature to have a mean of
37.5 degrees with a standard deviation of 0.6 degrees, based on samples of 100. A
sample of 100 refrigerators have an average temperature of 37.53 degrees. Are the
refrigerators within the 90% confidence interval?
No, the temperature is outside the confidence interval of (37.40, 37.60)
Yes, the temperature is within the confidence interval of (37.40, 37.60)
No, the temperature is outside the confidence interval of (36.90, 38.10)
Yes, the temperature is within the confidence interval of (36.90, 38.10) - Yes, the
temperature is within the confidence interval of (37.40, 37.60)
What is the 97% confidence interval for a sample of 204 soda cans that have a mean
amount of 12.05 ounces and a standard deviation of 0.08 ounces?
(12.033, 12.067)
(11.970, 12.130)
(11.970, 12.130)
(12.038, 12.062) - (12.038, 12.062)
Determine the minimum sample size required when you want to be 98% confident that
the sample mean is within two units of the population mean. Assume a standard
deviation of 5.75 in a normally distributed population.
43
45
23
, 44 - 45
Determine the minimum sample size required when you want to be 80% confident that
the sample mean is within 1.3 units of the population mean. Assume a standard
deviation of 9.24 in a normally distributed population.
83
194
195
84 - 83
Determine the minimum sample size required when you want to be 75% confident that
the sample mean is within thirty units of the population mean. Assume a standard
deviation of 327.8 in a normally distributed population
324
158
197
157 - 158
In a sample of 8 high school students, they spent an average of 24.8 hours each week
doing sports with a standard deviation of 3.2 hours. Find the 95% confidence interval.
(24.10, 25.50)
(22.66, 26.94)
(21.60, 28.00)
(22.12, 27.48) - (22.12, 27.48)
In a sample of 15 stuffed animals, you find that they weigh an average of 8.56 ounces
with a standard deviation of 0.07 ounces. Find the 92% confidence interval.
(8.526, 8.594)
(8.543, 8.577)
(8.528, 8.591)
(8.521, 8.599) - (8.526, 8.594)
Market research indicates that a new product has the potential to make the company an
additional $3.8 million, with a standard deviation of $1.8 million. If this estimate was
based on a sample of 10 customers, what would be the 90% confidence interval?
(3.06, 4.54)
(2.00, 5.60)
(2.51, 5.09)
(2.76, 4.84) - (2.76, 4.84)
Supplier claims that they are 95% confident that their products will be in the interval of
20.45 to 21.05. You take samples and find that the 95% confidence interval of what they
are sending is 20.32 to 21.48. What conclusion can be made?
The supplier is more accurate than they claimed
The supplier products have a lower mean than claimed
The supplier is less accurate than they have claimed
ANSWERS GRADED A+ 2025/2026
If a confidence interval is given from 8.52 to 10.23 and the mean is known to be 9.375,
what is the maximum error?
0.428
1.710
0.855
8.520 - 0.855
Which of the following is most likely to lead to a large margin of error?
small mean
large sample size
small sample size
small standard deviation - small sample size
From a random sample of 41 teens, it is found that on average they spend 31.8 hours
each week online with a population standard deviation of 3.65 hours. What is the 90%
confidence interval for the amount of time they spend online each week?
(30.86, 32.74)
(29.99, 33.61)
(24.50, 39.10)
(28.15, 35.45) - (30.86, 32.74)
A company making refrigerators strives for the internal temperature to have a mean of
37.5 degrees with a standard deviation of 0.6 degrees, based on samples of 100. A
sample of 100 refrigerators have an average temperature of 37.53 degrees. Are the
refrigerators within the 90% confidence interval?
No, the temperature is outside the confidence interval of (37.40, 37.60)
Yes, the temperature is within the confidence interval of (37.40, 37.60)
No, the temperature is outside the confidence interval of (36.90, 38.10)
Yes, the temperature is within the confidence interval of (36.90, 38.10) - Yes, the
temperature is within the confidence interval of (37.40, 37.60)
What is the 97% confidence interval for a sample of 204 soda cans that have a mean
amount of 12.05 ounces and a standard deviation of 0.08 ounces?
(12.033, 12.067)
(11.970, 12.130)
(11.970, 12.130)
(12.038, 12.062) - (12.038, 12.062)
Determine the minimum sample size required when you want to be 98% confident that
the sample mean is within two units of the population mean. Assume a standard
deviation of 5.75 in a normally distributed population.
43
45
23
, 44 - 45
Determine the minimum sample size required when you want to be 80% confident that
the sample mean is within 1.3 units of the population mean. Assume a standard
deviation of 9.24 in a normally distributed population.
83
194
195
84 - 83
Determine the minimum sample size required when you want to be 75% confident that
the sample mean is within thirty units of the population mean. Assume a standard
deviation of 327.8 in a normally distributed population
324
158
197
157 - 158
In a sample of 8 high school students, they spent an average of 24.8 hours each week
doing sports with a standard deviation of 3.2 hours. Find the 95% confidence interval.
(24.10, 25.50)
(22.66, 26.94)
(21.60, 28.00)
(22.12, 27.48) - (22.12, 27.48)
In a sample of 15 stuffed animals, you find that they weigh an average of 8.56 ounces
with a standard deviation of 0.07 ounces. Find the 92% confidence interval.
(8.526, 8.594)
(8.543, 8.577)
(8.528, 8.591)
(8.521, 8.599) - (8.526, 8.594)
Market research indicates that a new product has the potential to make the company an
additional $3.8 million, with a standard deviation of $1.8 million. If this estimate was
based on a sample of 10 customers, what would be the 90% confidence interval?
(3.06, 4.54)
(2.00, 5.60)
(2.51, 5.09)
(2.76, 4.84) - (2.76, 4.84)
Supplier claims that they are 95% confident that their products will be in the interval of
20.45 to 21.05. You take samples and find that the 95% confidence interval of what they
are sending is 20.32 to 21.48. What conclusion can be made?
The supplier is more accurate than they claimed
The supplier products have a lower mean than claimed
The supplier is less accurate than they have claimed
