The theoretical probability is how many times it SHOULD land on heads. Since there is two sides, the theoretical l probability says it should land on heads 10 times out of 20 or 1/2. The experimental probability can vary, it is how many times it ACTUALLY lands on heads when you test it. In this case it landed on heads 4 times out of 20 or 1/5 of the time. For this problem, the experimental probability is less than the theoretical probability.