Probability is the number of a certain event realization ($ N_x $) in terms of total number of all events realization ($ N $), which is mathematically represented as follows:

- $ P(X_i) = \frac{N_{X_i}}{N_{all}}, i=1,2,...,N $

where $ \sum_{i=1}^{N} P(X_i) = 1 $ since $ \sum_{i=1}^{N} N_{X_i} = N_{all} $.

For example, in dice the probability of event 1 is 1/6 because the number of all events is 6 and event 1 is one of all six events. As more simple example, the probability of coin face is close to 1/2 if the coin is normal.

## Applications of probabilityEdit

If we know the probability of any event, we can handle issues related to the event without long time experience of the event. For example, when we bet a money based on the special dice which produce output with different probabilities such as 0.1, 0.2, 0.3, 0.3, 0.2, 0.1 for 1, 2, 3, 4, 5, 6, respectively, we can put more money for 3 and 4 because these two values will give higher chances for win.