What value is subtracted from the number of data values (n) to get the degrees of freedom for a t-distribution?
1
What is the appropriate situation to use a t-distribution?
D.
A confidence interval is used to infer the sample average.
False
What values are inside a properly made confidence interval?
C.
What is the value of the sample average in the confidence interval below?
(96, 118)
(96 + 118) / 2 = 107
What is the value of the margin of error in the confidence interval below?
(96, 118)
(118 - 96) / 2 = 11
A local college instructor gave a statistics exam to his class of 31 students where the exam scores were normally distributed with an average score of 80 and a standard deviation score of 10. A competing college knew all their students scored 85 on this test. What is the 95% confidence interval to help find out how these local college students did in comparison to the competing college students?
C.
jQuery112402707462288058995_1711840973181
A local college instructor gave a statistics exam to his class of 31 students and calculated a 95% confidence interval for the exam scores of (77.1, 82.9). A competing college knew all their students scored an average of 85 on this test. How did the local college do in comparison to the competing college?
A.
The height of 14 students in a local college statistics course was measured and found to have an average height of 68 inches and a standard deviation height of 2 inches. What is the 90% confidence interval for the mean height of all students at the college?
A. (67.0, 68.9)
B. (67.3, 68.7)
C. (66.9, 69.0)
D. (67.7, 68.2)
CI = X ± Z * (σ/√n)
(z= z-score of 90%, 0.05 all the way at bottom)
= 68 + 1.645 * (2/√14)
= (67.0, 68.9)
The height of 14 students in a local college statistics course was measured and found to have a 90% confidence interval of (65.9, 69.9). Is the mean height of all the students at this local college 5 feet 6 inches or higher?
B.
The ages of 21 people in a local elder care home had an average age of 80 years and a standard deviation age of 8 years. What is the 99% confidence interval for the mean age of all people in elder care homes?
A.
CI = X ± Z * (σ/√n)
(75.0, 85.0)
The ages of 21 people in a local elder care home were measured and a 99% confidence interval of (76.6, 83.4) was calculated. Is the mean age of all people in elder care homes greater than 75 years old?
B.
The population mean must be known to calculate a confidence interval.
True
False
False
A fishery graduate student wanted to know the mean length of the perch in a local lake, so she caught 10 perch and measured their length. She found that these perch had an average length of 3.6 inches and a standard deviation length of 1.39 inches. What is the 95% confidence interval for the mean length of the perch in the lake?
A.
CI = X ± Z * (σ/√n)
In 2015 on the National Assessment of Educational Progress (NAEP) science scale:
- 15 black students had an average score of 125 and a standard deviation score of 5.81, while
- 15 Hispanic students had an average score of 136 and a standard deviation score of 3.87.
Please make two 98% confidence intervals to see if it is reasonable that students of these two races had the same population mean score
C.
An automotive engineer wants to estimate the cost of repairing a car that experiences a 25 MPH head-on collision. He looked up 24 car crashes and found that the average repair cost was $11,000 with a standard deviation cost of $2,500. Please find the middle and spread of a 98% confidence interval for the true mean repair cost.
B.
Find 1% (0.01) and 23 df on the t-chart.
= 2.500
Plug into equation:
11,000 + 2.5(2,500 / √24)
= 11,000 + 1,275
91 eggs were randomly chosen from a gravid female salmon and individually weighed. The average weight was 0.978 grams with a standard deviation weight of 0.042 grams. Please find the middle and spread of a 90% confidence interval for the weight of all salmon eggs.
B.
Find 5% (0.05) and 90 df.
= 1.662
Plug in:
0.978 + 1.662(0.042 / √91)
= 0.978 + 0.007
61 simple random samples of the local college's student body were collected and the number of people preferring their left hand was recorded. These samples had an average of 16 people preferring their left hand with a standard deviation of 4 people. Find a 95% confidence interval for the true proportion of left-handed people in the local college's student body.
B.
CI = X ± Z * (σ/√n)
Find the population mean age of victims of chain snatching during the last year for a sample of size 35 with an average age of 34.25 years and a standard deviation age of 10 years. Use a 96% confidence level.
