74. A curious number. Find such a positive number that $\frac{1}{5}$ of it, multiplied by its $\frac{1}{7}$, equals this number.
74. If $(N: 5)(N: 7)=N$, then $N(N-35)=0$, so $N=35$. In other words, if the given number is multiplied by itself, the result will be 35 times greater than if we multiply $\frac{1}{5}$ of this number by $\frac{1}{7}$ of it. Therefore, the number we are looking for is 35.

In the general case, if a number equals $\prod_{i=1}^{k}\left(\frac{1}{a_{i}}\right.$ of this number), then it equals $\left(\prod_{i=1}^{k} a_{i}\right)^{\frac{1}{(k-1)}}$