Students ranked from 1 to 5 will be interviewed by A and thus are moved to the waiting room X.Similarly, students ranked 6 to 15 (10 students) will be interviewed by B and are moved to waiting room Y.And students ranked 16 to 30 (15 students) will be interviewed by C and are moved to waiting room Z.A takes a break after every 3 interviews. B and C take breaks after every 5 and 4 interviews respectively.So, a map of the first few students will look like:Here, M, N, X and Y are the ranks of the students. M to M+4 are the set of 5 students who will be interviewed once the interview of the student ranked 5th gets over and similarly for others.We see that interviewer A finishes his first batch of interviews first (at 10:20) and hence M must be 31. Students ranked 31 to 35 move to waiting room X.Next to finish interviewing his/her first batch of interviewees is B (at 10:30) and hence Y=36. Students ranked from 36 to 50 will move into waiting room Z.Finally, interviewer Y will get the next 10 students ranked from 51 to 60 and hence X=51.We do not require N.Interviewer A interviews students ranked from 1 to 5, 31 to 35.Interviewer B interviews students ranked from 6 to 15 and 51 to 60.Interviewer C interviews students ranked from 16 to 30 and 36 to 50.An updated table will look like:We can break down the interviews of students ranked 41 to 50 for interviewer C as:Each set of 4 consecutively ranked students will be interviewed in 20 minutes. The fifth student will be interviewed after 20+5(break) minutes= 25 minutes.So, the interview of student ranked 41 starts at 11:05 am and that of student ranked 45 starts at 11:05+25= 11:30 am. Similarly the interview of student ranked 49 starts at 11:55 am and so on.