14. Scores for a statistics test are normally distributed with an average of 62 and a variance of 225. If the instructor wishes to award Bs or higher to the top 30% of students in the class, what score is required a B or higher?
a. 68.7 b. 71.5 hp. 73.2 d. 74.6 and 69.9
The answer is E, but I don’t know why.
2. Suppose the test scores of 600 students are normally distributed with mean 76 and variance
out of 64. The number of students scoring between 70 and 82 is:
a. 272 BC. 164 BC. 260 d. 136th. 328
The answer is E but I don’t know why. 14. Gap = SD^2
Z = (score-mean)/SD = (score-62)/15
Find a chart in the back of your stats text titled something like “areas under normal distribution” to find the proportion (.30) to give you the Z-score. Put that value into the equation above to find the score.
Z = ([70 or 82]-76)/8
Use the Z scores in the same table to find the proportions between them and multiply by 600.