My preference for these cases was always to learn the table of fractions-decimals until 1/20. It takes a little while, but can come in handy in a ton of cases.

For example, I always remember that 1/14 = ~0.07, and this has come in handy multiple times (even on the actual job, when brainstorming and having to do a "rough order of magnitude" calculation).

As a final point - don't stress too much about appearing clever on percentages with interviewers. I've had candidates who clearly were strong at Math, but at every point there was a number in the interview they tried to somehow "impress" me by their arithmetic prowness. You should still practice this, of course, but there are more important aspcets of the case you should focus on.

My preference for these cases was always to learn the table of fractions-decimals until 1/20. It takes a little while, but can come in handy in a ton of cases.

For example, I always remember that 1/14 = ~0.07, and this has come in handy multiple times (even on the actual job, when brainstorming and having to do a "rough order of magnitude" calculation).

As a final point - don't stress too much about appearing clever on percentages with interviewers. I've had candidates who clearly were strong at Math, but at every point there was a number in the interview they tried to somehow "impress" me by their arithmetic prowness. You should still practice this, of course, but there are more important aspcets of the case you should focus on.