A student attempts x number of questions. He answers 15 correctly out of the first 20 questions and of the remaining questions, he answers 1/3 correctly. If all questions have the same credit and the student gets 50% marks, then find the value of x.

1) Student attempts x questions.
2) Out of 20 questions he answered 15 correctly and of (x – 20) questions he answered 1/3 correctly.
3) The student gets 50% marks.
Therefore,
15 + 1/3(x – 20)= 50% of x
⇒ 15 + 1/3(x – 20) = (50/100) × x
⇒ 15 + 1/3(x – 20) = x/2
⇒ 90 + 2(x - 20) = 3x
⇒ x = 50
Hence, the number of questions attempted by the students = 50.