2025 MATH 221 STATISTICS QUESTIONS WITH ANSWERS
GRADED A+ 2025/2026
Determine the minimum sample size required when you want to be 95% confident that
the sample mean is within two units of the population mean. Assume a population
standard deviation of 4.3 in a normally distributed population.
20
22
16
18 - 18
Determine the minimum sample size required when you want to be 99% confident that
the sample mean is within 0.50 units of the population mean. Assume a population
standard deviation of 2.9 in a normally distributed population.
130
224
223
129 - 224
In a sample of 10 CEOs, they spent an average of 12.5 hours each week looking into
new product opportunities with a sample standard deviation of 4.9 hours. Find the 95%
confidence interval. Assume the times are normally distributed.
(7.6, 17.4)
(9.5, 15.5)
(9.4, 16.4)
(9.0, 16.0) - (9.0, 16.0)
In a sample of 18 kids, their mean time on the internet on the phone was 28.6 hours
with a sample standard deviation of 5.6 hours. Which distribution would be most
appropriate to use, when we assume these times are normally distributed?
z distribution as the sample standard deviation always represents the population
t distribution as the sample standard deviation is unknown
t distribution as the population standard deviation is unknown while the times are
assumed to be normally distributed
z distribution as the population standard deviation is known while the times are
assumed to be normally distributed - t distribution as the population standard deviation
is unknown while the times are assumed to be normally distributed
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
GRADED A+ 2025/2026
Determine the minimum sample size required when you want to be 95% confident that
the sample mean is within two units of the population mean. Assume a population
standard deviation of 4.3 in a normally distributed population.
20
22
16
18 - 18
Determine the minimum sample size required when you want to be 99% confident that
the sample mean is within 0.50 units of the population mean. Assume a population
standard deviation of 2.9 in a normally distributed population.
130
224
223
129 - 224
In a sample of 10 CEOs, they spent an average of 12.5 hours each week looking into
new product opportunities with a sample standard deviation of 4.9 hours. Find the 95%
confidence interval. Assume the times are normally distributed.
(7.6, 17.4)
(9.5, 15.5)
(9.4, 16.4)
(9.0, 16.0) - (9.0, 16.0)
In a sample of 18 kids, their mean time on the internet on the phone was 28.6 hours
with a sample standard deviation of 5.6 hours. Which distribution would be most
appropriate to use, when we assume these times are normally distributed?
z distribution as the sample standard deviation always represents the population
t distribution as the sample standard deviation is unknown
t distribution as the population standard deviation is unknown while the times are
assumed to be normally distributed
z distribution as the population standard deviation is known while the times are
assumed to be normally distributed - t distribution as the population standard deviation
is unknown while the times are assumed to be normally distributed
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
