1. Experiments on learning in animals sometimes measure how long a laboratory rat takes to find its way through a maze. Suppose for one particular maze, the mean time is known to be 20 seconds with a standard deviation of σ = 2 seconds. Suppose also that times for laboratory rats are Normally distributed. A researcher decides to test whether rats exposed to cigarette smoke take longer on average to complete the maze. She exposes 25 rats to cigarette smoke for 15 minutes and then records how long each takes to complete the maze. The mean time for these rats is 20.6 seconds. Are these results significant at the α = 0.05 level? Assume the researcher's rats can be considered an SRS from the population of all laboratory rats.
A. Yes
B. No
C. The question cannot be answered since the results are not practically significant.
2. Suppose the average Math SAT score for all students taking the exam this year is 480 with standard deviation 100. Assume the distribution of scores is normal. The senator of a particular state notices that the mean score for students in his state who took the Math SAT is 500. His state recently adopted a new mathematics curriculum and he wonders if the improved scores are evidence that the new curriculum has been successful. Since over 10,000 students in his state took the Math SAT, he can show that the P-value for testing whether the mean score in his state is more than the national average of 480 is less than 0.0001. We may correctly conclude that
A. there is strong statistical evidence that the new curriculum has improved Math SAT scores in his state.
B. although the results are statistically significant, they are not practically significant, since an increase of 20 points is fairly small.
C. these results are not good evidence that the new curriculum has improved Math SAT scores.
3. Suppose the average Math SAT score for all students taking the exam this year is 480 with standard deviation 100. Assume the distribution of scores is normal. A SRS of four students is selected and given special training to prepare for the Math SAT. The mean Math SAT score of these students is found to be 560, 80 points higher than the national average. We may correctly conclude
A. the results are not statistically significant at level α = 0.05, but they are practically significant.
B. the results are statistically significant at level α = 0.05, but they are not practically significant.
C. the results are neither statistically significant at level α = 0.05 nor practically significant.