In a class of 108 students the ratio of boys and girls is 5 : 4. If the number of boys increased by 3 and some girls also increased then the ratio becomes 7 : 6. How many girls were increased.

Total number of students = 108

The ratio of boys and girls is 5 : 4

$5+4=9\underset{\_}{\times 12}108$

$5\underset{\_}{\times 12}?60\to boys$

$4\underset{\_}{\times 12}?48\to girls$

The number of boys increased by 3 i.e. 60 + 3 = 63

Boys : Girls

63      :    54 (48 + 6)

7        :  6 girls increased by 6, then ratio becomes 7 : 6