The total number of students in a school was 660. The ratio

The total number of students in a school was 660. The ratio between boys and girls was 13 : 9. After some days, 30 girls joined the school and some boys left the school and new ratio between boys and girls became 6 : 5. The number of boys who left the school is :

In the first case,

Boys = 660 ×	13	= 390
	22

Girls = 660 ×	9	= 270
	22

If x boys leave the school, then

390 − x	=	6
270 + 30	=	5

⇒ 390 – x = 360
⇒ x = 390 – 360 = 30