Combinatorics questions- can someone please help?

I have a few questions relating to combinatorics, they're all in the imgur link below. If you could help, it would be much appreciated!

  • Hey just confirming that its only the two questions correct? I am having trouble accessing the link again for some reason

  • Thanks for reaching out. There should be five problems, #3,4,5,6 and 7. Here is the correct link.

  • You were very helpful last time, I appreciate your help again.


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  • Are you sure about #7? I was expecting an answer similar to this: Otherwise, awesome. I trust your judgement, just asking.

  • Hey - you are absolutely correct. Mine is correct until I used the "order matters" formula at the very end where it clearly doesn't apply here. If you follow the (correct) formula listed in your example, you get 20c4 =4,845 - which makes a lot more sense then what I originally put. My apologies for the confusion

  • Thanks for all your help!

The answer is accepted.