MAmean score/standard deviation/distribution table

HI! Can someone please explain to me how do I calculate questions like this one? The results of an accountancy exam are normally distributed with a mean score of 58 and a standard deviation of 10. What is the percentage probability that a student will score more than 80 (to 2 decimal places)? OR A probability of 2.28% will have been determined from the normal distribution table. The normal distribution value which will give this probability is 0.4772 (0.5 - 0.0228) This value equates to a Z-score of 2 from the normal distribution table. Z-score = (x - µ)/? 2 = (90 - 70)/? ? = 20/2 = 10 I am just looking for some formula someone could explain it to me. I keep having these kind of questions. I have already ask John one of these questions but I havent really understand anything from his answer. Just now I had again similar question in Mock test The number of daily complaints to a local government office has a standard deviation of 7 and the coefficient of variation is 20%. What is the mean number of daily complaints? Is there any videos, resources etc which could explain it to me step by step. Thank you