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      Question

      The average weight of a class of 25 student is 60 KG. If

      X is student joined the class,  than the average weight of whole class increases by (2X – 7)Kg. Find the value of X if the weight of whole class increases by 390 KG.
      A 5 Correct Answer Incorrect Answer
      B 2 Correct Answer Incorrect Answer
      C 6 Correct Answer Incorrect Answer
      D 7 Correct Answer Incorrect Answer
      E 4 Correct Answer Incorrect Answer

      Solution

      Sum of weights of 25 student = 25*60 = 1500 kg Sum of the weights of (25+x)(60+2x-7) = {(25+x)(53+2x)} kg As per the question  (25+x)(53+2x)-1500 = 390 (25+x)(53+2x) = 1890 2x2+103x-565=0 X= 5 or (-113/2) Student since the number of student cannot be negative. So our answer will be 5

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