Rounding numbers and simplifying calculations in case interviews is alsways a good idea as it minimises your risk of making a calculation error, and it also makes you faster at answering the question.
The tricky thing about rounding numbers is that if you round them too much you risk a) distorting the final result / finding, and b) your interviewer telling you to round the numbers less.
Rounding numbers is more of an art than science, but in our experience the following two tips tend to work well:
- We usually recommend to not round numbers by more than +/- 10%. This is a rough rule of thumb but gives good results based on conversations with past candidates.
- You also need to alternate between rounding up and rounding down so the effects cancel out. For instance, if you're calculating A x B, we would recommend rounding A UP, and rounding B DOWN. You get the idea!