The difference between the maximum value and the minimum value of a set of data is 80. If the group spacing is 9, the number of groups should be (C.9) A, 7 B, 8 C, 9 D, 10.
There are 400 students in grade seven in a school. In order to understand the eyesight of these students, a sample survey was conducted on the eyesight of 20 students, and the obtained data were sorted out. In the obtained frequency distribution table, if the frequency of data in the group of 0.95~ 1. 15 is 0.3, it can be estimated that the number of seventh-grade students with vision in the range of 0.95~ 1. 15 is about (120) a.