In a school, there are 550 students. The ratio of the boys to that of the girls is 6 : 5. How many more girls should join the school so that the ratio becomes 5 : 6?

110

Boys : Girls

 6     :   5

⇒ (6 + 5) units = 550

⇒ 11 units = 550

⇒ 1 unit = 50

⇒ No. of boys = 6 x 50 = 300

⇒ No. of Girls = 5 x 50 = 250.

⇒ No. of girls that should join the school so that the ratio becomes 5 : 6

⇒ 5 units = 300

⇒ 1 unit = 60,

⇒ Therefore, 6 units = 6 x60 = 360

⇒ No. of Extra girls joined = 360 - 250 = 110.