Exercise 3.30 1. In City A, there are 60 secondary schools with 250 sections in total. Suppose that all the sections have 25 boys and 25 girls each. Among the sections, 100 are Social Science stream and 150 are Natural Science stream. You want to select 30 sections from them to conduct a survey about the desired future occupation of the students. a. In this case, what are the strata? b. If you have to choose 30 sections as your sample, how many sections you should choose from Social Science stream and Natural Science stream, respectively?​