The average playing time of compact discs in a large collection is 35 min, and the standard deviation is 5 min.
a. What value is 1 standard deviation above the mean? 1 standard deviation below the mean? What values are 2 standard deviations away from the mean?
b. Without assuming anything about the distribution of times, at least what percentage of the times are between 25 and 45 min?
c. Without assuming anything about the distribution of times, what can be said about the percentage of times that are either less than 20 min or greater than 50 min?
d. Assuming that the distribution of times is normal, approximately what percentage of times are between 25 and 15 mph. A histogram revealed that the vehicle speed at impact distribution was approximately normal.
a. Roughly what proportion of vehicle speeds were between 27 and 57 mph?
b. Roughly what proportion of vehicle speeds exceeded 57 mph?