Multiple choice

In an exam, the average marks obtained by the students was found to be 60. After omission of computational errors, the average marks of 100 candidates had to be changed from 60 to 30 and the average with respect to all the examinees came down to 45 marks. The total number of candidates who took the exam, was एक परीक्षा में, छात्रों के द्वारा प्राप्त औसत अंक 60 पाए गए | संभावित त्रुटि को हटाने के बाद, 100 अभ्यर्थियों का औसत परिवर्तित होकर 60 से 30 हो गया और सभी परीक्षार्थियों के सापेक्ष औसत घटकर 45 अंक हो गया | कुल अभ्यर्थियों की संख्या जिन्होंने परीक्षा दी, थी

  1. 200

  2. 210

  3. 240

  4. 180
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A Correct answer
Explanation

Using alligation method: 100 students with average 30 are mixed with (n-100) students with average 60 to get overall average 45. The ratio is (60-45) : (45-30) = 15 : 15 = 1 : 1. So n-100 = 100, giving n = 200. Alternative: (100×30 + (n-100)×60)/n = 45 gives same result.

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