Total number of persons =30 Number of boys =20 Number of girls =20 Number of teachers =20 In committee of 30 people, participation of boys, girls and teachers is equal. ∴ Number of ways of selecting committees = Number of selection of 10 boys out of 20x Number of selection of 10 girls out of 20× Number of selection of 10 teacher out of 20 =20C10×20C10×20C10 =