12. Recall from Chapter 7 that the interquartile range covers the middle 50% of the data. For a bell-shaped population:

a. The interquartile range covers what range of standardized scores? In other words, what are the standardized scores for the lower and upper quartiles?

(Hint: Draw a standard normal curve and locate the 25th and 75th percentiles using Table 8.1.)

b. How many standard deviations are covered by the interquartile range?

c. The whiskers on a boxplot can extend a total of 2 interquartile ranges on either side of the median (which for a bell-shaped population is equal to the mean). Beyond that range, data values are considered to be outliers. At what percentiles (at the upper and lower ends) are data values considered to be outliers for bell-shaped populations?