There are 150 students in a school. If the ratio of the number of boys to girls is 4 : 1, then what is the mean proportion between the number of boys and girls in the school?

50 40 30 60

60

Boys : Girls = 4 : 1, ⇒ (4 + 1)units = 150, ⇒ 5 units = 150, ⇒ 1 unit = 30. ⇒ Boys = 4 x 30 = 120, Girls = 1 x 30 = 30. ⇒ Mean proportion = √120 x 30 = √3600 = 60.