Bob took a quiz consisting of 500 questions with two options: Yes and No. Bob did not prepare for the quiz. Flustered, he hastily reached for a fair coin in his wallet and started to toss this coin for answers. Whenever the coin landed heads, he shaded Yes; whenever the coin landed tails, he shaded No. It turned out that 40% of the questions have Yes as the correct answer, and the rest have No as the correct answer. Among those questions that Bob shaded Yes, roughly how many percent did he get correct?
A) 30% B) 40% C) 50% D)60% E) 70%
My thought is that of the questions he put as Yes, the chance of getting the right answers is equal to 40%. But this is just a guess and I'm not sure of the explanation or if this is the right answer.