There are two ways to calculate probability:
- using math to predict
- by actually observing the event and keeping score.
Theoretical probability uses math to predict the outcomes. Just divide the favorable outcomes by the possible outcomes.
Experimental probability is based on observing a trial or experiment, counting the favorable outcomes, and dividing it by the total number of times the trial was performed.
Let's look at this example: we tossed a coin 36 times and recorded the outcomes:
H, T, H, H, T, T, H, T, T, T, T, T,
T, T, T, H, H, T, H, H, T, H, H, H,
H, T, H, H, T, H, H, T, H, H, T, H
Based on this experiment:
- Experimental probability of flipping Heads is
or about 
and Tails is 
or about 
- Theoretical probability of flipping Heads is
and Tails is