A survey records the number of story books read last year by each of 20 students. The results are shown below.
Number of books : 1 2 3 4 5 6
Frequency : 2 4 6 3 3 2
(a) Find the cumulative frequency corresponding to each number of books.
(b) Identify the two middle positions in this data set.
(c) Calculate the median number of books read and state its value.