(b) 2*(5-1)! = 2*4! = 2*24 = 48 ways (considering circular permutations only, traditionally for such kind of problems) (d) If prizes are distinguishable (as it follows from the context), then the answer is 10*9*8 = 720 ways. (e)= 10 handshakes boys with boys PLUS = 10 handshakes girls with girls PLUS 5*4 = 20 handshakes boys with girls = 10 + 10 + 20 = 40 handshakes, in all.