Why in solving numerals of NDB and VOR, do we apply variation at the station in case of VOR and at the aircraft in case of NDB?
The reason is, that for a VOR, the receiver in the aircraft determines the radial based on calculating the phase shift and as the VOR is oriented to the magnetic north of its location, we need the variation of the station. Think of it as a lighthouse which changes the color through a full turn and hence you can just tell by the color, which radial you are on.
For the NDB however, the ADF receiver uses a sense/loop antenna to determine a direction and the needle is overlaid onto a course card which is oriented to the magnetic north of the aircraft. Think of it as a pilot looking out of the window to see a lighthouse that has a white omnidirectional light.
So as you can see the angle is once determined at the VOR and once from the aircraft and hence the different variations apply. Nevertheless I think this was espacially emphasized for examination, as it is not that important in practical flying nowadays.