# Unique combinations in a set.(+)

by Solumsen
Tags: combinations, unique
 P: 1 Hey there! I will start of with saying I´m not very good at English when considering mathematical terms, neither an expert in Math. My question goes as this: I have a set of 1000 questions - which will be given in rounds with a set of 10. So every round, you get 10 questions out of the 1000. We want to change out 5 questions in every round. So we want to have not only to have the total number of combinations where 1 question is unique - but where a set of 5 is. Please, if the formulation is a bit misleading - i will try to clarify in a reply. As i said, this is even hard for me to question in the right way! - Thanks in advance
 Sci Advisor HW Helper Thanks PF Gold P: 26,122 Hey Solumsen! Welcome to PF! I don't understand … you want 10 questions, each of which has not been asked before … but that automatically means that any 5 of them will not have been asked before
 P: 384 The number of unique sets of 5 would be 1000!/(5!*995!). The number of unique sets of 10 would be 1000!/(10!*990!). The number of unique ways of grouping all unique sets of 10 into two groups of 5 would be (10!/(2*5!*5!))(1000!/(10!*990!)). Since I can't quite figure out what the problem is, I don't know if any of this helps.

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