You have to divide a group of three girls and six boys into a group of four and a group of five. In how many ways can you do this?

Hi! Thanks! I'm kind of confused though this isn't a fraction right? How does this mean 126?

I’m sure Rom will carefully explain this to you.

No it is combination maths. C for combination or C for choice

9C4 = 9C5     

The brackets that Rom used is just another way to display this.

There is a C function on any 'proper' calculator.

9C4 means how many different combinations of 4 items can I choose if I have 9 items altogether to choose from.