3.64 For the sample data presented in the dotplot of Exercise 3.63, construct a frequency distribution in which the classes are 10–under 20, 20–under 30, and 30–under 40. If this frequency distribution were all that we knew about the underlying data, what approximate values would be estimated for the mean and standard deviation of these data?

( DATA SET ) Note: Exercises 3.65–3.69 require a computer and statistical software.