Question

4/7 of the children in the hall are girls and the rest are boys. If there are 12 more girls
than boys, how many children are there in the hall?

Answer 1

If we take the total number of children in the hall as C, then,

Number of girls = (4/7)C
Number of boys = (3/7)C

We've also been given the difference, so:
(4/7)C - (3/7)C = 12
=> (4/7 - 3/7)C = 12
=> (1/7)C = 12
=> C = 12*7
=> C = 84

Answer 2

Thank you very much, Arora :].