I was told that they would be conducting an HR interview but the interviewer dropped a market sizing question which was not aforementioned in the earlier email conversation. I was not aware that this question time can appear already as this generally falls under as a case-study or question.

There are 5 rounds of the interview process. 1) paper test: it was multiple choice includes Problem solving, GMAT, IQ Test (logical reasoning) 2) group discussion with HR: We were given a case study to crack with about 5-6 people in the team. During this process, HRs look how you work in the team such as your teamwork skill, communication and flexibility. 3) HR interview: it was 1-1 interview. Each of the candidate interviewed with different person. 4) case interview with 2 head of department ( I interviewed with Ex-Mckinsey. The case interview was similar to top 3 consulting firms do for their interview.) 5) group discussion with head of departments as assessors