In a test every correct answer earns 4 marks and every wrong answer loses 1 mark. A student who knows nothing about a question guesses at random among its 4 options. What is his expected mark on that question?

The guess is right with probability 1/4 and wrong with probability 3/4, so the expected mark is (1/4)(4) + (3/4)(−1) = 1 − 0.75 = 0.25 — a small but real gain, which is why random guessing pays under this marking scheme. Answering 0 assumes the reward and the penalty cancel, which would need a penalty of 4/3 marks; 1 keeps only the reward part and 0.75 only the penalty part.