C

Find the limit: $$\underset{n\to \mathrm{\infty }}{lim}(\frac{1}{3}+\frac{1}{9}+\cdots +\frac{1}{3^n})$$.

A swimming pool can be filled by two pipes in $5$ hours. It takes $24$ hours longer to fill the pool by only the first pipe than by only the second one. In how many hours does the first pipe fill the pool, in how many hours does the second one? Find the sum of both times.

The surface area of a cuboid is $11776{\mathrm{cm}}^2$. Its dimensions are in the ratio $3:5:1$. Find the volume of the cuboid.

If $x\in (0;1)\cup (1;\mathrm{\infty })$ then the product $({\log }_{x}3)({\log }_{5}x)$ can be written as: