Can't tell the difference between permutation and combination In an exam, a student has to answer 6 out of 8 questions. How many ways can she answer the 6 questions if 
a) there are no restrictions?
b) The first 3 questions are compulsory?
c) she must answer at least 3 of the first  4 questions?
I am confused. Why is this question combination? I thought it is supposed to be a permutation. The 6 questions that the student is supposed to answer are specific. For example, each question is unique on its own. That is my understanding, but its wrong ._. Can anyone correct my logic?
 A: a) There are $\binom{8}{6}$ possibilities.
b) He can only choose 3 question among the 5 last, i.e. $\binom{5}{3}$.
c) He can choose 3 questions among the 4 first and 2 questions among the last 4 or 4 question among the four first and 2 among the 4 last, i.e. $$\binom{4}{3}\binom{4}{3}+\binom{4}{2}.$$
Why are you talking about permutation ?
A: I'm not giving actual answers but trying to resolve your confusions.
I wouldn't say the questions are 'specific'.  Each one is either answered or not answered, but the statistically important bit is that they are added together in aggregation for consideration (answer $6$ questions in total).  Thus, for example, answering question number $123678$ is same as $123876$; the order (i.e. permutations) doesn't matter (e.g. answering which ones first).
Hope it helps.
A: Consider a finite set $A$, so $\exists$ natural $n$: $|A|=n$, there  are no problems thinking $A$ as $\{1,2,...,n\}$. Let's define permutations and combinations:
Permutations of ${A}:=\big\{ f: \{1,2,...,n\} \rightarrow \{1,2,...,n\}$ bijective$\big\}$
Combinations of $k$ elements extract form $A:=\big\{ S \subseteq A: |S|=k\big\}$ 
Very importatnt facts: 


*

*You can think a permutation of $A$ as a $n$-tuple with all different entries because of a bijection (e.g: let $A=\{1,2,3\}$. $(2,1,3)$ represent the permutation $f: f(1)=2$ etc). In $n$-tuples order matter.

*Combinations are sets (subset of $A$)! When you consider a set order doesn't matter.

