Find the expected point value of a random guess, is there anything to gain or lose on average by guessing? . please answer with specifics , if you cannot think of any examples you may use this one:

the test is multiple choice. each question has four possible answers. the test taker must select one answer for each question or not answer the question. 10 points are rewarded for each correct response and 10 points are subtracted for each wrong answer or for answers left blank. what is the expected point value of a random guess? is it advantageous to guess?