Have another question for you today:
A course has seven elective topics, and students must complete exactly three of them in order to pass the course. If 200 students passed the course, show that at least 6 of them must have completed the same electives as each other.
Now I know this is related to counting and the pigeonhole principle, and there are a couple of other related questions already asked but I couldn't apply them to my quuestion.
I know that the (informal) pigeonhole principle states that if you have $n$ boxes, and you have more than $n$ pigeons to distribute between those boxes, then at least one of the boxes will contain more than one pigeons, but I'm not sure what my boxes and what my pigeons are in this problem