Answer: We should ASSUME 1/2 or 50%
Step-by-step explanation: Since we don't know the exact number of times the person flipped the coin, we must infer you mean he/she flips the coin once. So, If a coin has 2 sides and the probability is 100% total, we can write an expression to help us solve:
P(Probability)= 100/2
P= 50% or 1/2
How I got 50% or 1/2 is I took the whole probability (100%) and divided it by 2. (2 sides on a coin)
I hope this helped (at least)