the theoretical probability is a fancy term for an even amount of both, which would be 20 flips landing on H, and 20 landing on T. Since the question is asking what's the difference between the theoretical probability and the experimental results, you'd take 20(theoretical number of flips that land on H) and subtract 15 (experiment results for the amount of flips that land on H), and 20 - 15 = 5. Now that you know the difference is 5, you would divide 5 by 40 to find the answer. 5/40 = 1/8 when you simplify, making the answer D.
