## Online Course Discussion Forum

### Question on II-A

Question on II-A

How would you write a bijection (7.25)?

Re: Question on II-A

One-to-one, with every one of them used up.  (Hint: Look at 7.4b in lecture.)

Re: Question on II-A

You need to associate each way to arrange the $n$ identical balls into the $k$ boxes to a solution of the equation $a_1 + \cdots + a_k = n$, and vice versa.