To find probability, you must divide the number of events by the number of possible outcomes.
An event (or favorable outcome) is an outcome that is desired.
An outcome is one of many things that could happen.
Since the events occur two times, they must be doubled.
In this case, there are 400 possible outcomes and 20 number of events.
The probability of you playing one of your top 10 favorite songs for 2 days is 0.05.
