What is the theoretical probability of getting heads? that's it nothing else just it like 50/50 shot? or 1/2?

The theoretical probability of getting heads is just 50/50, you were right.

When you are flipping a coin, there are two equally likely possible outcomes. Only 1 of those outcomes is heads.

Therefore, the theoretical probability of getting heads is 1/2, or 0.5 or 50% or we often just say 50/50.

The answer is 90 % because since 20 multiplied by 5 is 100 you would have to do each question multiplied by 5 so 18 times 5 equals ninety percent.