On the below question, how did they decided the two probabilities of guessing the correct and wrong answer on a question? Where did the 0.25 and 0.75 come from?

The probability of achieving exactly k successes in n trials is shown below.

Formula:

n = number of trials

k = number of successes

n - k = number of failures

p = probability of success in one trial

q = 1 - p = probability of failure in one trial

Example: You are taking a 10 question multiple choice test. If each question has four choices and you guess on each question, what is the probability of getting exactly 7 questions correct?

n = 10

k = 7

n - k = 3

p = 0.25 = probability of guessing the correct answer on a question

q = 0.75 = probability of guessing the wrong answer on a question