# Resolved: Combinatorics Practice Exam

Practice exam for Combinatorics, question 6 states the formula for combinations without repetition is:

(n + p -1)! / p!

Whereas the course videos and notes show:

(n + p -1)! / (n -1)!p!

Hey Christopher,

Thank you for your comment!

In the explanation of the exercise, the 'n-choose-k' notation is used. It is defined in the following way:

Therefore:

Hope this helps!

Kind regards,

365 Hristina

Thanks for the explanation Hristina,

I took a look back over the course notes and this method isn't described in the PDF under combinations with repetition. I also went back to check the video, but note that there isn't actually a video for combinations with repetition and there is just reference to download the course notes.

Can you please point me to where you found this formula, was it in the 365DS course material anywhere?

Hey Christopher,

It seems like we have missed to include the definition of the 'n-choose-k' notation in the course notes. We will update them as soon as possible!

Thank you for your contribution!

Kind regards,

365 Hristina