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Let the no of correct answer be x than marks he got for correct answer be 4x . No of wrong answers and unanswered be (180-x) marks deducted be -1(180-x) now total marks = 450 => 4x -(180-x) = 450 => 5x = 450 +180 => 5x = 630 => x= 630/5 => x= 126 => he answered 126 question correctly