Question

What is the probability of rolling 7 or a 5 on a single 10 sided dice

Answer 1

Here a "success" is "obtaining a 7 or a 5."  Assuming that the 10-sided die is marked {1, 2, 3, ... , 9, 10}, there are 2 ways in which to get a "success" out of 10 possible outcomes.  Thus, P(5 or 7) is 2/10, or 1/5, or 02.