In a school there were 1554 students and the ratio of the number of the boys and girls was 4 : 3, After few days, 30 girls joined the school but few boys left; as a result the ratio of the boys and girls became 7 : 6. The number of boys who left the school is

Given that, In a school there were 1554 students and the ratio of the number of the boys and girls was 4 : 3.

If we consider number of boys as x and number of girls as y

=> x:y= 4:3

From the ratio and total number of students, we can determine that x=888 & y=666

If 30 girls joined the school and number of boys left is considered as "a"

=> $$ 888-a : 666+30 = 7:6 $$

=> $$ 888-a = \frac {7}{6} \times 696 $$

=> $$ 888-a=812 $$

=> $$ a=76 $$

Therefore, Number of boys left the school are 76.