Tell me about a time when you made a mistake.. How did you find it and what did you do to correct it? (On the job, school work, recipe, etc)

There was a time when I was in high school and I had a Math test. I did all the tasks in the test and was sure I answered everything correctly. However, just before I was about to submit the test, I saw that I forgot to add the minus sign (-) in one of the results. I quickly corrected my mistake and successfully submitted my test. In the end, I got an A as I really answered everything correctly.