Let the number of right answers be ‘a’ and number of wrong answers be ‘b’

Given, Yash scored 40 marks in a test, getting 3 marks for each right answer and losing 1 mark for each wrong answer. Had 4 marks been awanded for each correct answer and 2 marks been deducted for each incorrect answer, then Yash would have scored 50 marks

⇒ 3a – b = 40 ------ (1)

4a – 2b = 50 ---- (2)

Multiplying eq1 by 2 and subtracting eq2 from it

⇒ 6a – 4a = 80 – 50

⇒ a = 15

Thus, 45 – b = 40

⇒ b = 5

Total number of questions in the test = 15 + 5 = 20