After investigation, there are many bank depositors in a village, and the frequency of depositors with deposits between 20,000 yuan and 30,000 yuan is 0.2. And the sum of the frequency of deposits for other depositors is 40, so there are _ _ 10 _ _ households with deposits between 20,000 yuan and 30,000 yuan in this village.

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.