Question 574528
Use the combination formula


C(n,r) = (n!)/(r!(n-r)!)


C(15,3) = (15!)/(3!*(15-3)!)


C(15,3) = (15!)/(3!*12!)


C(15,3) = (15*14*13*12!)/(3!*12!)


C(15,3) = (15*14*13)/(3!)


C(15,3) = (15*14*13)/(3*2*1)


C(15,3) = (2730)/(6)


C(15,3) = 455


So 455 different groups can be made.