Answer:
Step-by-step explanation:
Intial ratio of Boys to Girls is 12/10 --> 6/5
on 6 boys joining the class turns total number of boys to be 18 boys
and let say number of girls is g
for ratio to remain same
6/5= 18/g
g=18*5/6
g=15
So the number of girls that need to join is 5