Probability is the likelihood that an event will occur. It is written as a fraction with the number of favorable outcomes as the numerator and the total number of outcomes as the denominator.

Theoretical probability is the probability that is calculated using math formulas. This is the probability based on math theory.

Experimental probability is calculated when the actual problem is performed as an experiment. In this case, you would perform the experiment, and use the actual results to determine the probability.

In order to accurately perform an experiment, you must:

·       Identify what constitutes a "trial".

·       Perform a minimum of 25 trials

·       Set up a table or chart to record your data.

Let’s look at an example.

When asked about the probability of a coin landing on heads, you would probably answer that the chance is ½ or 50%. Imagine that you toss that same coin 20 times. How many times would you expect it to land on heads? You might say, 50% of the time, or half of the 20 times. So you would expect it to land on heads 10 times. This is the theoretical probability.

The theoretical probability is what you expect to happen, but it isn't always what actually happens. The table below shows the results after John tossed the coin 20 times. 

The experimental probability of landing on heads is 13/20 = 65%. It actually landed on heads more times than we expected. Now, John continues to toss the same coin for 50 total tosses. The results are shown below. 

Now the experimental probability of landing on heads is 26/50 = 52%. The probability is still slightly higher than expected, but as more trials were conducted, the experimental probability became closer to the theoretical probability.