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प्रश्न
In a competitive examination, one mark is awarded for each correct answer while `1/2` mark is deducted for every wrong answer. Jayanti answered 120 questions and got 90 marks. How many questions did she answer correctly?
उत्तर
Let the number of correct answers be x then the number of wrong answers be (120 – x)
Then, by given condition,
`x xx 1 - (120 - x) xx 1/2` = 90
⇒ `x - 60 + x/2` = 90
⇒ `(3x)/2` = 150
∴ x = `(150 xx 2)/5`
= 50 × 2
= 100
Hence, Jayanti answered correctly 100 questions.
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