A total of n balls are to be put into k boxes with the conditions that there will be n1 balls in box I, n2 balls in box 2, and so on, with nk balls being placed in box k (n1 + ... + nk = n) Explain why the number of ways of doing this is
n! / n1! × ... × nk!
Explain why this is just Cnn1 = Cnn2 when k = 2.