A little topology (I think) problem here:
For A:= [0,1) ∪ ([2,3] ∩ ) ∪ {5} ⊂ R (real numbers) find the closure, boundary and interior of A
I know the definitions but I don't know how to actually calculate them
To compute the closure, just notice that the closure of a finite union is the union of the closures.
For the interior, can the points of $\displaystyle \left[2,3\right]\cap \mathbb Q$ be in it? And what about $\displaystyle \left\{5\right\}$?