Consulting firms use case interviews to evaluate candidate's analytical ability and problem-solving skills; they are looking not for a "correct" answer but for an understanding of how the applicant thinks and how the applicant approaches problems.
[1] During case interviews, interviewers are generally looking for the following skills:[2] Candidates are often asked to estimate a specific number, often a commercial figure (such as market size or profitability) or determine action plans to remedy a business problem (such as low profitability or decreasing market share).
Candidates are expected to demonstrate reasoning rather than to produce the exact answer.
Here several candidates are given some briefing materials on a business problem and asked to discuss and agree upon a solution.
They assess candidates' communication and interaction as well as analytical thinking and commercial awareness.