Your parabola has the form ax^2+bx+c if a>0 then it is open towards the positive y direction, for a<0 towards the negative y direction This also means that with a>0 a global minimum exists and for a<0 a global maximum So by changing a from a>0 to a<0 the parabola previously had a maximum and now has a minimum instead, which is the first option.
Yes because you would pay less if the 20% was taken off first because it would be a lower amount since your taking a percent of the whole total and not combining the two
