AR, I don't know what you are flying but V Speeds are definitely calculated ! They are calculated carefully and tabled in flight manuals etc to be compliance with performance regulations.
They are based on numerous factors A/C weight, runway length available, OAT, PA etc
This question has been posed as it was asked on a performance exam.
It may be just that it is badly worded.
I think Mad Scientist is the closest with:
OK, Vr-V2 speed spread will increase on a colder day, because the thrust will be higher (unless you're totally 'flat rated') which will provide more acceleration at a given weight.
Thanks for the replies guys & gals