Question

If all the girls danced but only two-thirds of the boys danced how many children danced in all

Answer 1

5/6 of the children
I feel as if there is information missing from the question though such as quantities.

Answer 2

If theres 43 kids, 25 girls and 18 boys... 
If 2/3rds of all the boys danced than that's 12 
If all the girls danced thats 25
12+25= 37

37 kids danced, then.