Maybe I am miss understanding this persons math here but why would I expect a 50% increase in my speed to translate to a 50% reduction in my travel time? I wou

Maybe I am miss understanding this persons math here but why would I expect a 50% increase in my speed to translate to a 50% reduction in my travel time? I would expect a 100% increase in my speed to translate to a 50% reduction in my travel time. Or more clearly put, double my speed, halve by travel time. Not considering relativity, is not speed defined by change in distance over change in time? That is linear is it not?