Verified Answer :

We are simply trying to select any 12 girls from the 24 girls.

Here the order in which the 12 girls are arranged does not matter.

So this is a combination problem.

So the answer is 24 combination 12.

24 Combination 12 =    24! / ((24 - 12!)12!)
        
                               =     24! / ( (12!)12!)
 
                     =  2423 2221201918171625141312! / (12!12!) 
 
                     =  2423 222120191817162514*13 / 12!
                          
Use a calculator.

                     = 2704156  different groups