Multiple choice

The average weight of a group of boys and girls is 57 kg. The average weight of the boys is 60 kg and that of the girls is 52 kg. If the number of boys is 25, then find the number of girls.

  1. 17

  2. 16

  3. 15

  4. 12

  5. 14
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let B=25, G be number of girls. Total weight = 57(25+G). Boys weight = 60*25 = 1500. Girls weight = 52G. 1500 + 52G = 57(25+G) => 1500 + 52G = 1425 + 57G => 75 = 5G => G = 15.

AI explanation

Use the method of allegations to find the ratio of boys to girls. The overall average is 57, the boys average is 60, and the girls average is 52, so the ratio is (57 minus 52) to (60 minus 57), which is 5 to 3. Since there are 25 boys representing 5 parts, each part equals 5 students. Multiplying the 3 parts for girls by 5 gives 15 girls.

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