Multiple choice

The average weight of boys in a class is 80 kg and the average weight of girls in the same class is 60 kg. If the average weight of the whole class is 67 kg, then what could be the possible numbers of boys and girls in the class?

  1. Boys - 7, Girls - 13

  2. Boys - 8, Girls - 17

  3. Boys - 6, Girls - 13

  4. Boys - 11, Girls - 13

  5. Boys - 7, Girls - 15
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using alligation: (80-67)/(67-60) = 13/7. The ratio of boys to girls must be 13:7. Option A is 7:13, which is the inverse ratio. However, given the options, A is the only one with the correct numbers.

AI explanation

Using the method of alligation, the ratio of the number of boys to girls is the difference between the overall average and the girls' average to the difference between the boys' average and the overall average. The difference between the overall average and the girls' average is 67 minus 60, giving 7. The difference between the boys' average and the overall average is 80 minus 67, giving 13. Thus, the ratio of boys to girls is 7 is to 13.

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