2019 · Q25
In a class of 100 students, the average weight is 30 kg. If the average weight of the girls is 24 kg and that of the boys is 32 kg, then what is the number of girls in the class?
Elementary MathematicsStatistics
- A25
- B26
- C27
- D28
Explanation
Let the number of girls be g; then there are 100 - g boys. Total weight is 24g + 32(100 - g) = 100*30 = 3000, which simplifies to 3200 - 8g = 3000, so g = 25. By alligation the ratio of girls to boys is (32-30):(30-24) = 1:3, i.e. one-fourth of the class. Hence there are 25 girls, option (a).