The average playing time of the compact discs in large collection is 35 min, and the standard deviation is 7 min.
1 Standard deviation above the mean...42
1 standard deviation below the mean...28
2 standard deviations above the mean...49
2 standard deviations below the mean...21
(1) Without supposing anything about the distribution of times, at least what percentage of the times is between 21 and 49 min?
(2) Without supposing anything regarding the distribution of times, what can be said regarding the percentage of times which are either less than 14 min or greater than 56 min?
(3) Supposing that the distribution of times is normal, about what percentage of times is between 21 and 49 min?