Given we have to form 4 mixed pairs for tournament i.e. we need 4 boys and 4 girls..
So we can select 4 boys from 5 in C(5,4) = 5 ways
and also we can select 4 girls from 5 in 5 ways..
So by multiplication principle of counting , we have :
No of ways of making mixed pair team = 5 * 5 = 25
Hence number of possible selections = 25