Any line segment can be divided continuously ad infinitum At all times with each division the length of each part shortens by a half while at the same time the number of parts multiplies by two So how can an infinite number of parts no matter how small they are make up a finite whole Because for every division not just some but all the lengths of the parts are reducing as fast as the number of parts are increasing  This means that even as the number of divisions tends to infinity the corresponding halving of each part keeps the original line segments length intact