In an examination, a student scores 3 marks for every correct answer and looses 1 marks for every wrong answer. A student attempted all the 120 questions and scored 320 marks. Find the number of questions, he answered incorrectly.

10

The correct answer is Option (2) → 10

Let:

$x$ = number of correct answers

$y$ = number of wrong answers

We are told:

$x+y=120$ (total questions)

and the scoring rule gives:

$3x−1y=320$

Now solve these two equations.

From the first equation:

$y=120−x$

Substitute into the second:

$3x−(120−x)=320$

Simplify:

$3x−120+x=320$

$4x=440$

$x=110$

Hence,

$y=120−110=10$

Number of incorrect answers = 10