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There are * * * ninth grade students in a school. In order to understand the physical condition of the students in this grade, some students were randomly selected for skipping test, and four students, A, B, C and D, were appointed to sort out the data of the test results. The following figure is part of the information provided by these four students:

A: Group all test data and draw a histogram (as shown in the figure);

B: Students who skip rope more than 100 times account for100%;

C: First, the sum of the two groups of frequencies is, and both the first and second groups of frequencies are;

D: Frequency ratios of the first, second and third groups.

According to the materials provided by these four students, please answer the following questions:

How many students did you choose for this advanced placement exam? How many people are in each group?

If the number of skipping rope is not less than two times, according to the results of this spot check, what is the estimated number of people with excellent skipping performance in the whole grade?

Taking the median of each group (the data corresponding to the midpoint of each group) as the representative of this group of truancy times, the average truancy times of these students are estimated.