Huh? 50 is halvtreds (20 * 2.5)
70 is actually halvfjerdensindstyve, literally "half to the four(th20) times 20". So the base number (20) * 3.5...
The problem is, Danish people can't understand each other even with the simplest of words, so they just say halvfjerds.
Me neither. But it's an easy solution, just fill the tube with some toilet paper for extra padding.