Multiple choice

In a class of $100$ students there are $70$ boys whose average marks in a subject are $75$. If the average marks of the complete class is $72$, then what is the average of the girls?

  1. $73$
  2. $65$
  3. $68$
  4. $74$
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B Correct answer
Explanation

Total marks for 100 students = 100 * 72 = 7200. Boys' total marks = 70 * 75 = 5250. Girls' total marks = 7200 - 5250 = 1950. Number of girls = 30. Average of girls = 1950 / 30 = 65.

AI explanation

The total marks for the entire class are 100 multiplied by 72, which equals 7200. The total marks for the 70 boys are 70 multiplied by 75, which equals 5250. The total marks for the 30 girls (100 minus 70) are 7200 minus 5250, which equals 1950; dividing 1950 by 30 gives the girls' average, making the result 65.

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