Final answer:
The probability of success in a single trial is represented by the symbol 'p'.
Step-by-step explanation:
The symbol used to represent the probability of success in a single trial is p. In a binomial experiment, where there are only two possible outcomes (success and failure), the probability of success on one trial is denoted by the letter p. The probability of failure on one trial is denoted by the letter q. Both probabilities add up to 1, so p + q = 1.