a box contains 15 balls (4 yellow, 5 purple, 6 blue) 3 balls are drawn at random...

without replacement ..calculate P( all 3 balls are of the same color)

The solution says it should be (4/15)^3 + (5/15)^3 +(6/15)^3

I think it should be (4*3*2)/(15*14*13)...Anyone can explain it to me?

Thanks a lot!