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Q: Three maths classes: A, B and C take an algebra test. The average score of class A is 83. The average score of class B is 76. The average score of class C is 85. The average score of class A and B is 79 and average score of class B and C is 81. What is the average score of classes A, B, C ?

  • 1
    81
  • 2
    78
  • 3
    80.5
  • 4
    81.5
  • Show Answer
  • Workspace

Answer : 4. "81.5"
Explanation :

Answer: D) 81.5 Explanation: Let the number of students in classes A, B and C be P, Q and R respectively.Then, total score of A = 83P, total score of B = 76Q, total score of C = 85R.Also given that,(83P + 76Q) / (P + Q) = 79=>4P = 3Q.(76Q + 85R)/(Q + R) = 81=>4R = 5Q,=>Q = 4P/3 and R = 5P/3Therefore, average score of A, B, C = ( 83P + 76Q + 85R ) / (P + Q + R) = 978/12 = 81.5

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