# Homework Help: Combinations Problem

1. Oct 14, 2005

### amcavoy

I was thinking that I could solve this with combinations. However, I am unsure of how to use it in this case. If I remember correctly, the combinations are given by:

$$\begin{pmatrix}n \\ r\end{pmatrix}=\frac{n!}{r!\,\left(n-r\right)!}$$

Hmm. Any thoughts on this? Am I on the right track with the above?

Thanks.

2. Oct 14, 2005

### Tide

There are $2^{10}$ ways of selecting the digits and $_{10}C_3$ ways of having three 1's.

3. Oct 14, 2005

### amcavoy

Alright. I was thinking that it didn't matter if they were the same number; I could still use the formula above. Thanks for the confirmation .