Multiple choice

In an examination, the average marks of girls is 73 and the average marks of boys is 71. The average marks of girls and boys together is 71.8. What is the percentage of boys ?

  1. 58

  2. 60

  3. 55

  4. 40

  5. 45
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B Correct answer
Explanation

Using the alligation method: Let the ratio of girls:boys be x:y. Then 73x + 71y = 71.8(x+y). Solving gives 73x + 71y = 71.8x + 71.8y, which simplifies to 1.2x = 0.8y, so x/y = 2/3. This means girls:boys = 2:3, so boys = 3/(2+3) = 3/5 = 60%.

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