Multiple choice

Three Science classes A, B and C take a Life Science 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 classes A and B is 79 and the average score of classes B and C is 81. Then, the average score of classes A, B and C is

  1. 81.5

  2. 80

  3. 80.5

  4. 81
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AI explanation

From the average of A and B, we write 83A plus 76B equals 158A, which simplifies to 25A equals 2B. From the average of B and C, we write 76B plus 85C equals 162B, which simplifies to 11C equals 2B, making A, B, and C proportional to 2, 25, and 22 respectively. The combined average score is 83 times 2, plus 76 times 25, plus 85 times 22, all divided by 49, which equals 3992 divided by 49, resulting in 81.5.

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