Community Forum
Ask anything about cases, applications and recruiting. Members and coaches answer.
How accurate does mental math need to be in a case interview?
- Mental Math
Do interviewers expect mental math to be basically perfect, or is there tolerance for a small arithmetic mistake if your setup is right and you catch it? I am much more worried about accuracy than speed right now.
Accuracy matters, but one small arithmetic error is not automatically fatal if your setup is sound and you recover cleanly.
How much rounding is acceptable in case interview math?
- Mental Math
When doing case math, how aggressively can you round? I know estimation is encouraged, but I worry that rounding too early will push the final answer far enough off that it looks sloppy.
Round when it materially simplifies the calculation and the case does not require high precision. The goal is to preserve the business conclusion while reducing unnecessary arithmetic.
How do I stop making stupid calculation mistakes under pressure?
- Mental Math
My math speed is improving, but I still make annoying mistakes when I feel rushed. Usually it is not a big conceptual error, just dropping a zero or messing up a simple percentage. Any tips for reducing those under-pressure mistakes?
Build a short checking habit into your process. Before you say the final number, pause for one beat and ask yourself whether the magnitude makes sense, whether the sign is right, and whether you kept track of units correctly.
Best way to improve mental-math speed for case interviews?
- Mental Math
I know I need to get faster at mental math, but I am not sure what the highest-yield practice actually is. Should I just grind random drills, or focus on certain types of calculations?
Targeted practice usually beats random practice. Focus first on the operations that appear constantly in cases: percentage changes, multiplication shortcuts, division, weighted averages, and break-even style calculations.