For a normal distribution curve with a mean of 21 and a standard deviation of 5, which range of the variable defines an area under the curve corresponding to a probability of approximately 68%? Select one: a. from 18.5 to 23.5 b. from 16 to 26 c. from 21 to 31 d. from 11 to 31 Solution 16 to 26 because area under curve is 68% means it should be b/w mean-std and mean+std.