Use the Normal Curve applet. The 68-95-99.7 rule for Normal distributions is a useful approximation. You can use the Normal Curve applet on the text Web site to see how accurate the rule is. Drag one flag across the other so that the applet shows the area under the curve between the two flags.
(a) Place the flags one standard deviation on either side of the mean. What is the area between these two values? What does the 68-95-99.7 rule say this area is?
(b) Repeat for locations two and three standard deviations on either side of the mean. Again compare the 68-95-99.7 rule with the area given by the applet.