20. A study of students taking Statistics 101 was done. Four hundred students who studied for more than 10 hours averaged a B. Two hundred students who studied for less than 10 hours averaged a C. This difference was significant at the 0.01 level. What does this mean?
A. The probability that the difference was due to chance alone is greater than 0.01.
B. There is less than a 0.01 chance that the first group’s grades were better by chance alone.
C. The improvement was due to the fact that more people studied.
D. There is not enough information to make any conclusion
21. Sample size = 400, sample mean = 44, sample standard deviation = 16. What is the margin of error?
A. 1.4 B. 1.6 C. 2.2 D. 2.6
Assuming a 95% confidence level, and noting that this class seems to use z = 2 for this confidence level instead of the more accurate 1.96 value.
E = z*s/√n = 2 * 16 / √400 = 1.6
22. Select the best fit line on the scatter diagram below.
|D. None of the lines is the line of best
23. A researcher wishes to estimate the mean amount of money spent per month on food by households in a certain neighborhood. She desires a margin of error of $30. Past studies suggest that a population standard deviation of $248 is reasonable. Estimate the minimum sample size needed to estimate the population mean with the stated accuracy.
A. 274 B. 284 C. 264 D. 272
Again, assuming a 95% confidence interval, with z = 2.00 instead of 1.96:
n = (z * s / E)2 = (2 * 248 / 30)2 = 273.35 à 274
24. Suggest the cause of the correlation among the data.
The graph shows strength of coffee (y) and number of scoops used to make 10 cups of coffee (x). Identify the probable cause of the correlation.