The question says that the speed is inversely proportional to the length. Thus, Inverse means, as the diameter increases, the speed reduces, or as the diameter reduces, the speed increases.
Thus, from the question, if diameter A is 20, and B is 10, then definitely, the speed will increase from 348 to a higher rate. Mathematically, we have
20 / 10 = 348 / x, where x is the missing speed.
2 = 348 / x
x = 348 / 2
x = 174 rpm
Therefore, the pulley A must have been running at a speed of 174 rpm
