Vladimir
This one is the one nearly every cultivation novels makes. Basically, every single cultivation method with a distance in a "blink of an eye" or "half of a breath" is flawed. What is also funny is when the MC and Arrogant Young Master#1 both have those special arts. Sometimes, both used their arts to their "full potential" but in the end, they managed to stay inside a small square of 50 meters length. Like seriously, what is read is like, roaming thousands of miles, jumping hundreds of meters in the sky, but in reality, they are barely moving at all. Specifically in "Tournament Arc", where the author specifically says that the dueling court is small because of everyone watching the battle.
At the same time, it is not necessarily an error in maths in that case. More like, to make the fight more interesting, close whatever adjective you can think of that will make it better. Instead of staying realist, they chose to break a little the reality to offer a better experience to the reader. When it is the stats and money and time of traveling of the MC, I think that's because they failed at remembering the exact number. But for the rest, it can be considered as making the novel more interesting.
It's like "increasing my power one fold", I never really understood what it meant. Sometimes, the MC can slaughter in one move the previously invincible enemy, sometimes he just barely beat it.