Question

In an examination, a student scores 4 marks for every correct answerand loses 1mark for every wrong answer. if he attempts all 90 questionsand secures 140 marks, the number of questions he attempts correctly, is:

Answer 1

Given, total questions = 90
Let the number of correct answers given by the candidate be 'x' and wrong answers by the candidate be 'y'
4 marks per correct answer, -1 mark per wrong answer

Given,
4*x - 1*y = 140....(i)
x + y =90....(ii)  [since he answered all the questions]
Add above 2 equations:
5x = 230
x= 46

So, Out of 90 questions, he attempted 46 questions correctly
Hope this helps